Understanding the lower GMP formation in large GTPase hGBP-2 and role of its individual domains in regulation of GTP hydrolysis.
The interferon γ-inducible large GTPases, human guanylate-binding protein (hGBP)-1 and hGBP-2, mediate antipathogenic and antiproliferative effects in human cells. Both proteins hydrolyse GTP to GDP and GMP through successive cleavages of phosphate bonds, a property that functionally distinguishes them from other GTPases. However, it is unclear why hGBP-2 yields lower GMP than hGBP-1 despite sharing a high sequence identity (~ 78%). We previously reported that the hGBP-1 tetramer is crucial for enhanced GMP formation. We show here that the hGBP-2 tetramer has no role in GMP formation. Using truncated hGBP-2 variants, we found that its GTP-binding domain alone hydrolyses GTP only to GDP. However, this domain along with the intermediate region enabled dimerization and hydrolysed GTP further to GMP. We observed that unlike in hGBP-1, the helical domain of hGBP-2 has an insignificant role in the regulation of GTP hydrolysis, suggesting that the differences in GMP formation between hGBP-2 and hGBP-1 arise from differences in their GTP-binding domains. A large sequence variation seen in the guanine cap may be responsible for the lower GMP formation in hGBP-2. Moreover, we identified the sites in the hGBP-2 domains that are critical for both dimerization and tetramerization. We also found the existence of hGBP-2 tetramer in mammalian cells, which might have a role in the suppression of the carcinomas. Our study suggests that sequence variation near the active site in these two close homologues leads to differential second phosphate cleavage and highlights the role of individual hGBP-2 domains in the regulation of GTP hydrolysis.
['Rajan|Sudeepa|S|', 'Pandita|Esha|E|', 'Mittal|Monika|M|', 'Sau|Apurba Kumar|AK|']
D000595:Amino Acid Sequence D020134:Catalytic Domain D019204:GTP-Binding Proteins D006157:Guanosine Monophosphate D006160:Guanosine Triphosphate D006367:HeLa Cells D006801:Humans D006868:Hydrolysis D008958:Models, Molecular D011487:Protein Conformation D000072417:Protein Domains D055503:Protein Multimerization D017385:Sequence Homology
large GTPase guanine cap tetramerization allosteric regulation conformational change