Nucleotides released

Strittmatter SM, Valenzuela D, Sudo Y, Linder ME, Eishman MC (1991) An intracellular guanine nucleotide release protein for Go. GAP-43 stimulates isolated alpha subunits by a novel mechanism. J Biol Chem 266 22465-22471... 

Ebinn, J.O., Bottorf, D.A., Chan, E.Y.W., Stang, S.L., Dunn, R.J. and Stone, J.C. RasGRP, a ras guanyl nucleotide-releasing protein with calcium- and diacylglycerol-binding motifs (1998) Science 280,1082-1086... 

Hu P, Margolis B, Skolnik EY et al. Interaction of phosphatidylinositol 3-kinase-associated p85 with epidermal growth factor and platelet-derived growth factor receptors. Mo/ Cell Biol 1992 12 981-990. Li N, Batzer A, Daly R et al. Guanine-nucleotide-releasing factor hSosl binds to Grb2 and links receptor tyrosine kinases to Ras signalling. Nature 1993 363 85-88. 

Kimple, R. J., Kimple, M. E., Betts, L., Sondek, J., and Siderovski, D. P. (2002). Structural determinants for GoLoco-induced inhibition of nucleotide release by Galpha subunits. Nature 416, 878-881. 

Reubold, T., Eschenburg, F. S., Becker, A., Kull, F. J., and Manstein, D. J. (2003). A structural model for actin-induced nucleotide release in myosin. Nat. Struct. Biol. 10, 826-830. 

The specific effects of purified dnaj and grpE proteins on the dnaK protein have been characterized (Liberek et al., 1991a). The dnaj and grpE proteins, acting in concert, can stimulate the basal ATPase activity of dnaK 50-fold dnaj appears to enhance the rate of nucleotide hydrolysis by dnaK, but does not substantially affect nucleotide release. The grpE protein appears to enhance the rate of release of nucleotide bound to dnaK. Consequently, neither protein alone exerts a dramatic effect on the overall rate of ATP turnover by dnaK however, the effect of the two proteins combined is to accelerate both the rate of ATP hydrolysis and the rate of nucleotide release, resulting in enhanced ATP turnover. The concentrations of dnaj and grpE required for half-maximal effect are both 0.1-0.2 fiM. 

The first step in the activation of G proteins is the replacement of GDP by GTP. Whereas in the case of heterotrimeric G proteins, GDP-GTP exchange is catalysed by G-protein-coupled heptahelical receptors, monomeric G proteins, such as Ras, recruit GDP exchange factors (GEFs) and guanine nucleotide release proteins (GNRPs). These factors promote formation of the active, GTP-bound form of Ras and, because they are linkers, connect Ras with the RTK. 

H. Tbrasawa, D. Kohda, H. Hatanaka, S. Tsuchiya, K. Oguia, K. Nagata, et al. Structme of the N-terminal SH3 domain of GRB2 complexed with a peptide from the guanine nucleotide releasing factor SOS. Nature Struct Biol, 1, 891-897, 1994. 

S. Tanaka, T. Morishita, Y. Hashimoto, S. Hattori, S. Nakamura, M. Shibuya, et cd. C3G, a guanine nucleotide-releasing protein expressed ubiquitously, binds to the Src homology 3 domains of CRK and GRB2/ASH proteins. Proc Natl Acad Set, USA, 91 (8), 3443-3447, 1994. 

Sos, son of sevenless, is a Drosophila gene that encodes a guanine nucleotide release factor, which activates Ras. It is involved in neuronal development in Drosophila. 

Figure 1 Chemical mechanism of DNA polymerase and 3 -5 exonuclease, (a) DNA polymerase reaction. The enzyme chelates two metal Ions using three aspartic acid residues (only two are shown). Metal ion A abstracts the 3 hydroxyl proton of the primer terminus to generate a nucleophile that attacks the a-phosphate of an incoming dNTP substrate. The phosphoryl transfer results In production of a pyrophosphate leaving group, which is stabilized by metal Ion B. (b) The 3 -5 exonuclease proofreading activity is located in a site that is distinct from the polymerase site yet it uses two-metal-ion chemistry similar to DNA synthesis. The reaction type is hydrolysis in which metal ion A activates water to form the hydroxy anion nucleophile. Nucleophile attack on the phosphate of the mismatched nucleotide releases it as dNMP (dGMP in the case shown).

Gotoh T, Hattori S, Nakamura S, Kitayama H, Noda M, Takai Y, Kaubuchi K, Matsui H, Hatase O, Takahashi H, Kurata T, Matsuda M. Identification of Rapl as a target for the Crk SH3 domain-binding guanine nucleotide-releasing factor C3G. Mol. Cell. Biol. 1995 15 6746-6753. 

QUESTION 8.5 The reaction summary for gluconeogenesis is shown below. After examining the gluconeogenic pathway, account for each component in the equation. (Hint The hydrolysis of each nucleotide releases a proton.)... 

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