Determinants at the N- and C-termini of G[alpha].sub.12 required for activation of Rho-mediated signaling

• Published in: Journal of molecular signaling Vol. 8; pp. 3 - 5
• Main Authors: Ritchie, Benjamin J, Smolski, William C, Montgomery, Ellyn R, Fisher, Elizabeth S, Choi, Tina Y, Olson, Calla M, Foster, Lori A, Meigs, Thomas E
• Format: Journal Article
• Language: English
• Published: Ubiquity Press Ltd 25.03.2013
• Subjects: Binding proteins; G proteins; Leukemia; Protein binding; Purines
• ISSN: 1750-2187; 1750-2187
• DOI: 10.1186/1750-2187-8-3

Heterotrimeric guanine nucleotide binding proteins of the G12/13 subfamily, which includes the [alpha]-subunits G[alpha].sub.12 and G[alpha].sub.13 , stimulate the monomeric G protein RhoA through interaction with a distinct subset of Rho-specific guanine nucleotide exchange factors (RhoGEFs). The structural features that mediate interaction between G[alpha].sub.13 and RhoGEFs have been examined in crystallographic studies of the purified complex, whereas a G[alpha].sub.12 :RhoGEF complex has not been reported. Several signaling responses and effector interactions appear unique to G[alpha].sub.12 or G[alpha].sub.13 , despite their similarity in amino acid sequence. To comprehensively examine G[alpha].sub.12 for regions involved in RhoGEF interaction, we screened a panel of G[alpha].sub.12 cassette substitution mutants for binding to leukemia-associated RhoGEF (LARG) and for activation of serum response element mediated transcription. We identified several cassette substitutions that disrupt G[alpha].sub.12 binding to LARG and the related p115RhoGEF. These G[alpha].sub.12 mutants also were impaired in activating serum response element mediated signaling, a Rho-dependent response. Most of these mutants matched corresponding regions of G[alpha].sub.13 reported to contact p115RhoGEF, but unexpectedly, several RhoGEF-uncoupling mutations were found within the N- and C-terminal regions of G[alpha].sub.12 . Trypsin protection assays revealed several mutants in these regions as retaining conformational activation. In addition, charge substitutions near the G[alpha].sub.12 N-terminus selectively disrupted binding to LARG but not p115RhoGEF. Several structural aspects of the G[alpha].sub.12 :RhoGEF interface differ from the reported G[alpha].sub.13 :RhoGEF complex, particularly determinants within the C-terminal [alpha].sub.5 helix and structurally uncharacterized N-terminus of G[alpha].sub.12 . Furthermore, key residues at the G[alpha].sub.12 N-terminus may confer selectivity for LARG as a downstream effector.