Research Repository :: Browsing by Author "John, Jasson"

Browsing by Author "John, Jasson"

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Biological properties of Ha-ras encoded p21 mutants and mechanism of the autophosphorylation reaction
(1988-08) John, Jasson; Frech, Matthias; Wittinghofer, Alfred
Kinetic studies performed on p21H guanine nucleotide complexes with and without Mg2+ show that point mutations at positions 12, 59, and 61 each have a different effect on the rate of nucleotide dissociation. Double mutants with a combination of these amino acid substitutions reveal that the effects of each mutation on these kinetics are interactive (nonadditive) for positions 12 and 59 and approximately additive for the positions 12 and 61. The magnitude and direction of the effects seen are dependent on the nature of the nucleotide and whether or not the complexes contain Mg2+. All the mutants have reduced GTPase activity. It is also shown that the autophosphorylation reaction velocity is of first order with respect to the protein concentration and that this reaction is an intramolecular one, which takes place as a side reaction of the GTPase reaction. The autophosphorylation is not reversible under the experimental conditions. The covalently bound phosphate does not decrease the nucleotide-binding ability of the protein nor does it change the relative affinity of the protein for GTP versus GDP. The results are discussed in terms of the structural model and function of p21H.
Borasio, G.D. et al. ras p21 protein promotes survival and fiber outgrowth of cultured embryonic neurons. Neuron 2, 1087-1096
(1989-01) Borasio, Gian D.; John, Jasson; Wittinghofer, Alfred; Barde, Y. A.; Sendtner, Michael; Heumann, Rolf
Although evidence obtained with the PC12 cell line has suggested a role for the ras oncogene proteins in the signal transduction of nerve growth factor-mediated fiber outgrowth, little is known about the signal transduction mechanisms involved in the neuronal response to neurotrophic factors in nontransformed cells. We report here that the oncogene protein T24-ras, when introduced into the cytoplasm of freshly dissociated chick embryonic neurons, promotes the in vitro survival and neurite outgrowth of nerve growth factor-responsive dorsal root ganglion neurons, brain-derived neurotrophic factor-responsive nodose ganglion neurons, and ciliary neuronotrophic factor-responsive ciliary ganglion neurons. The proto-oncogene product c-Ha-ras also promotes neuronal survival, albeit less strongly. No effect could be observed with truncated counterparts of T24-ras and c-Ha-ras lacking the 23 C-terminal amino acids including the membrane-anchoring, palmityl-accepting cysteine. These results suggest a generalized involvement of ras or ras-like proteins in the intracellular signal transduction pathway for neurotrophic factors.
Characterisation of the metal-ion - GDP complex at the active sites of transforming and nontransforming p21 proteins by observation of the 17O-Mn superhyperfine coupling and by kinetic methods
(1987-01) Feuerstein, Juergen W.; Kalbitzer, Hans R.; John, Jasson; Goody, Roger S.; Wittinghofer, Alfred
Kinetic studies on the interaction of three Ha-ras-encoded p21 proteins with GDP and MgGDP have yielded values for the association (10(6)-10(7) M-1 s-1) and dissociation (10(-3)-10(-5) s-1) rate constants at 0 degrees C. Dramatic differences in the rate constants were not observed for the three proteins. Under non-physiological conditions (absence of Mg2+), the rate constant for GDP release was an order of magnitude faster for the viral protein p21v than for the cellular form p21c or the T24 mutant p21t, but this was reduced to a factor of about 3 in the presence of Mg2+. In all cases, there was an increase of about one order of magnitude in the rate of GDP release on removing magnesium. The binding affinities ranged from 5.7 X 10(10) M-1 for p21c to 1.3 X 10(11) M-1 for p21v. Electron paramagnetic resonance (EPR) measurements on Mn2+ bound together with stereospecifically 17O-labelled GDP showed direct coordination of a beta-phosphate oxygen to the metal ion with a superhyperfine coupling constant of 0.16-0.22 mT, but no interaction with the alpha-phosphate oxygens at the active site of all three proteins. The association constant of Mn(II) to p21 proteins in the absence of nucleotides was estimated to be greater than 10(5) M-1. In agreement with the EPR results, experiments on the metal ion dependence of the binding of thiophosphate analogs of GDP provided further evidence for the absence of direct coordination of the metal ion to the alpha-phosphate group. These results have been used to construct a model for the interactions of Mg X GDP with the active site of p21 proteins.
Checklist of Tanzanian Species, Version 1 HuldaGideon, PhilibertNyinondi and GodfreyOyema (eds), InterPress of Tanzania Ltd, Tanzania Commission for Science and Technology, Dar es Salaam (2012), 545 pp. ISBN: 978-9987-9485-1-2
(Wiley, 2015-11) John, Jasson
Tanzania is among the top biodiversity-rich countries inAfrica and a signatory to the Convention on BiologicalDiversity. Yet until recently, there has not been anycomprehensive documentation of the species of Tanzania.Before the production of the ‘Checklist of TanzanianSpecies’ by Gideon, Nyinondi and Oyema (2012), infor-mation was scattered in published and unpublished works,Web journals, and in the depositories of academic andresearch institution’s libraries, herbaria and museumswhere it was difﬁcult to access. This book is an importantcontribution to the documentation of Tanzanian biodiver-sity.Species accounts in this book are arranged by taxon(species totals in brackets); marine algae (556), amphi-bians (197), terrestrial arthropods (867), birds (1148),cnidarians (365), echinoderms (144), ﬁshes (1568), fungi(810), mammals (333), water molluscs (159), plants(7714 veriﬁed, 953 unresolved names), poriferans (120)and reptiles (355), with individual chapters co-authoredby experts from universities, research institutions andknowledgeable practitioners.Although most chapters are well written, some authorsdid not cross-check the species checklists with interna-tional databases, and hence, there are important omis-sions. Furthermore, the written accounts for several taxaalso do not relate closely to species checklist. For example,in the chapter on mammals, the authors discuss theedibility of species and whether a species is pest, but this isnot indicated in the species checklist. Similarly, in themammal and reptile chapters, the proportion of endemicand threatened species are cited, but no attempt is made toidentify the threatened or endemic status of individualspecies. In the mammal chapter, Equus burchelii is placed in
Crystallization and preliminary X-ray analysis of the human c-H-ras-oncogene product p21 complexed with GTP analogues
(Elsevier, 1989-03) Scherer, Anna; John, Jasson; Linke, Rosita; Goody, Roger S.; Wittinghofer, Alfred; Pai, Emil F.; Homes, K. C.
The catalytic domain (amino acid residues 1 to 166) of the human ras-oncogene product p21 complexed with the GTP analogues beta,gamma-imido-GTP (GMPPNP), beta,gamma-methylene-GTP (GMPPCP), and guanosine-5'-(gamma-thiotriphosphate) (GTP gamma S) have been been crystallized. Crystals of the GMPPNP and GMPPCP complexes are well suited for high resolution X-ray crystallography. They belong to space group P3(1)21 (or its enantiomorph P3(2)21) with unit cell axes a=b=40.3 A and c = 162.2 A.
First record of the association of Cattle Egret Bubulcus ibis with Shoebill Balaeniceps rex
(2012-11) John, Jasson; Lee, Woo S.
Association of Cattle Egrets Bubulcus ibis with large herbivores is well documented, but there are few records of their association with large birds. Here we describe the first-known records of foraging interactions between Shoebill Balaeniceps rex and Cattle Egrets. The observations were made at the Malagarasi-Muyovozi Ramsar Site in western Tanzania. Small flocks of egrets approached and foraged within 5 m of a Shoebill, which was sometimes forced to move from its hunting pool and by doing so it likely flushed more prey for egrets. Interactions occurred almost exclusively in the driest months, which suggested that prey were more difficult to locate by egrets during this period. The Shoebill inhabits inaccessible swamps and is a rare species with low density throughout its range. It is therefore possible that egret–Shoebill associations, in addition to being infrequent and highly seasonal, may have gone unnoticed.
International Action Plan for Spotted Ground Thrush Zoothera guttata
(2004-12) Ndang'ang'a, Paul K.; Buckley, Paul; Evans, Steven W.; Buckley, Paul; Newbery, P.; Hoffmann, D. A.; John, Jasson
BirdLife International is a global Partnership of people working for birds and the environment that is present in more than 100 countries. Over five million people support the BirdLife Partnership of national non-governmental conservation organisations (Partners) and local networks (Site Support Groups or IBA Caretakers). The BirdLife Partnership works together on shared priorities, programmes, and policies, learning from each other to achieve real conservation results. Each BirdLife Partner or Partner Designate represents a unique geographic area or territory (most often a country). In addition to Partners, BirdLife has Affiliates and a flexible system of working groups, (including some Bird Specialist Groups shared with Wetlands International and/or the Species Survival Commission (SSC) of the World Conservation Union (IUCN), each with specific roles and responsibilities. The BirdLife Partnership in Africa comprises 17 autonomous organisations in 18 countries that together have over 30,000 members and over 300 paid staff (see back cover).
Observations of threatened birds in the East Usambara Mountains, Tanzania
(2007-12) Borghesio, Luca; John, Jasson; Mulungu, Elia; Mkongewa, Victor; Joho, Martin P.; Cordeiro, Norbert J.
We report the preliminary observations and results of a survey of the birds of the East Usambara Mountains, north-east Tanzania. Using standardised point counts and opportunistic searches, we collected information on the distribution, habitat selection and relative abundance of those species of greatest conservation concern. Amongst the 124 species recorded during the survey, six are listed in the global Red Data book and nine are considered to be restricted-range. Forest edges and agricultural habitats had notable numbers of species of conservation importance. Habitat requirements of the species of conservation concern differed: whilst ground-foragers (Usambara Thrush Turdus (olivaceus) roehli, Modulatrix spp.) are clearly dependent on intact forest, Banded Sunbird Anthreptes rubritorques, Amani Sunbird Hedydipna pallidigastra, Fischer’s Turaco Tauraco fischeri, Kenrick’s Starling Poeoptera kenricki and Long-billed Tailorbird Artisornis moreaui are also frequent in successional habitats created by disturbance, at forest edges or even in relatively open, agricultural landscapes. This suggests that some threatened species might benefit from conservation initiatives (e.g., planting of useful indigenous trees) specifically targeted to counter the degradation of such ‘fringe’ habitats.
Observations on nesting of shoebill Balaeniceps rex and wattled crane Bugeranus carunculatus in Malagarasi wetlands, western Tanzania
(2013-02) John, Jasson; Nahonyo, Cuthbert L.; Lee, Woo S.; Msuya, Charles A.
The populations of shoebill Balaeniceps rex and wattled crane Bugeranus carunculatus are listed as ‘vulnerable’ by IUCN and threatened by habitat destruction and trapping (BirdLife International, 2012a). They both have narrow and disconnected distribution in sub-Saharan Africa along major water basins (Hancock, Kushlan & Kahl, 1992; Meine & Archibald, 1996). Their global population is small (<8000 birds for each species), and in Tanzania, numbers are in low hundreds (Dinesen & Baker, 2006; Beilfuss, Dodman & Urban, 2007). But yet, there is virtually no published information on nesting in Tanzania. The first and the only published breeding of wattled crane is that of Elliott (1983) from Southern highlands where wattled crane has almost been extirpated (Beilfuss, Dodman and Urban, 2007). Small viable populations for both species are found in Malagarasi wetlands. Basic ecological information of these threatened-flagship species is needed for both scientific and management purposes. In this article, we report observations of the first ground study on nests of shoebill and wattled crane in Tanzania, made between 2005 and 2011.
ras p21 protein promotes survival and fiber outgrowth of cultured embryonic neurons
(Elsevier, 2009-01) Borasio, Gian D.; John, Jasson; Wittinghofer, Alfred; Barde, Y. A.; Sendtner, Michael; Heumann, Rolf
Although evidence obtained with the PC12 cell line has suggested a role for the ras oncogene proteins in the signal transduction of nerve growth factor-mediated fiber outgrowth, little is known about the signal transduction mechanisms involved in the neuronal response to neurotrophic factors in nontransformed cells. We report here that the oncogene protein T24-ras, when introduced into the cytoplasm of freshly dissociated chick embryonic neurons, promotes the in vitro survival and neurite outgrowth of nerve growth factor-responsive dorsal rootganglion neurons, brain-derived neurotrophic factor-responsive nodose ganglion neurons, and ciliary neuronotrophic factor-responsive ciliary ganglion neurons. The proto-oncogene product c-Ha-ras also promotes neuronal survival, albeit less strongly. No effect could be observed with truncated counterparts of T24-ras and c-Ha-ras lacking the 23 C-terminal amino acids including the membrane-an-choring, palmityl-accepting cysteine. These results sug-gest a generalized involvement of ras or ras-like proteins in the intracellular signal transduction pathway for neurotrophic factors.
Status Report for the Eastern Arc Mountains and Coastal forests of Kenya and Tanzania Region, 2008
(2008-12) Ndang'ang'a, Paul K.; Eshiamwata, George; Ngari, A. N.; Pius, Exper; Arinaitwe, Julius; John, Jasson; Mbwana, Saidi
This report assesses the status of biodiversity in the Eastern Arc Mountains and Coastal Forests of Kenya and Tanzania (EACF) region against most of the 19 biodiversity monitoring indicators agreed upon by the stakeholders in the region. It uses information availed up to the end of 2008, and where possible comparisons made with past data to assess trends. This is done as part of an initiative geared towards instituting a standardised biodiversity monitoring system across the region. 2. Indicators are grouped in such a way that they assess STATE (changes in forest quality, cover, presence and abundance of threatened species, national legislation and ecosystem services), PRESSURE (changes in extraction intensity, human population and fire frequency) and RESPONSE (changes in forest management effectiveness, actions and research targeting key species and investment in the region) of the biodiversity in the EACF. 3. Forest disturbance data collected in 2005 and 2006 especially for Eastern Arc Mountain Forests is already showing clear differences in forest quality between differently-managed forest sites. It also provides useful baseline information for future monitoring of forest quality. For the few (6) sites where past comparative data exists, there is evidence of either stable (3 cases) or worsening (3 cases) forest quality in the past two to five years. Kaya Kinondo is probably one of the very few coastal forests where no disturbance was recorded over a long period - 13 years (1994-2007) of extensive field surveys. Further analysis shows that forest areas managed under joint and community-based forest management are recovering compared with forests managed by government alone, or under open access regimes. After 10 years of joint forest management implementation there is a dramatic decline in rates of cutting, indicating that participatory forest management is showing signs of delivering impact in terms of improved forest condition in Tanzanian forests at least. Forest health and condition measurements in parts of three areas of the Eastern Arc Mountains undertaken in 2000 and 2001 and re-measured in 2006 generally indicate that the measured trees were healthy. In one of the cases (Ngangao Forest in the Taita Hills) tree damages increased slightly over the survey period with stem decays constituting the most prominent symptom, but overall no significant change was found in this first re-measurement
Tucker, J. et al. Expression of p21 proteins in Escherichia coli and stereochemistry of th nucleotide-binding site. EMBO J. 5, 1351-1358
(1986-06) Tucker, J.; Sczakiel, Georg; Feuerstein, Juergen W.; John, Jasson; Goody, Roger S.; Wittinghofer, Alfred
v-Ha-ras encoded p21 protein (p21V), the cellular c-Ha-ras encoded protein (p21C) and its T24 mutant form p21T were produced in Escherichia coli under the control of the tac promoter. Large amounts of the authentic proteins in a soluble form can be extracted and purified without the use of denaturants or detergents. All three proteins are highly active in GDP binding, GTPase and, for p21V, autokinase activity. Inhibition of [3H]GDP binding to p21C by regio- and stereospecific phosphorothioate analogs of GDP and GTP was investigated to obtain a measure of the relative affinities of the three diphosphate and five triphosphate analogs of guanosine. p21 has a preference for the Sp isomers of GDP alpha S and GTP alpha S. It has low specificity for the Sp isomer of GTP beta S. Together with the data for GDP beta S and GTP gamma S these results are compared with those obtained for elongation factor (EF)Tu and transducin. This has enabled us to probe the structural relatedness of these proteins. We conclude that p21 seems to be more closely related to EF-Tu than to transducin.

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