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Analysis of GTPases carrying hydrophobic amino acid substitutions in lieu of the catalytic glutamine: Implications for GTP hydrolysis
Author(s) -
Mishra Rajeev,
Gara Sudheer Kumar,
Mishra Shambhavi,
Prakash Balaji
Publication year - 2005
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.20413
Subject(s) - gtpase , gtp' , glutamine , biochemistry , gtp binding protein regulators , chemistry , amino acid , protein structure , stereochemistry , g protein , signal transduction , enzyme
Ras superfamily GTP‐binding proteins regulate important signaling events in the cell. Ras, which often serves as a prototype, efficiently hydrolyzes GTP in conjunction with its regulator GAP. A conserved glutamine plays a vital role in GTP hydrolysis in most GTP‐binding proteins. Mutating this glutamine in Ras has oncogenic effects, since it disrupts GTP hydrolysis. The analysis presented here is of GTP‐binding proteins that are a paradox to oncogenic Ras, since they have the catalytic glutamine (Gln cat ) substituted by a hydrophobic amino acid, yet can hydrolyze GTP efficiently. We term these proteins HAS‐GTPases. Analysis of the amino acid sequences of HAS‐GTPases reveals prominent presence of insertions around the GTP‐binding pocket. Homology modeling studies suggest an interesting means to achieve catalysis despite the drastic hydrophobic substitution replacing the key Gln cat of Ras‐like GTPases. The substituted hydrophobic residue adopts a “retracted conformation,” where it is positioned away from the GTP, as its role in catalysis would be unproductive. This conformation is further stabilized by interactions with hydrophobic residues in its vicinity. These interacting residues are strongly conserved and hydrophobic in all HAS‐GTPases, and correspond to residues Asp92 and Tyr96 of Ras. An experimental support for the “retracted conformation” of Switch II arises from the crystal structures of Ylqf and hGBP1. This conformation allows us to hypothesize that, unlike in classical GTPases, catalytic residues could be supplied by regions other than the Switch II (i.e., either the insertions or a neighboring domain). Proteins 2005. © 2005 Wiley‐Liss, Inc.