Abstract
GTPases are important regulatory proteins that hydrolyze GTP to GDP. A novel GTP‐hydrolysis mechanism is employed by MnmE, YqeH and FeoB, where a potassium ion plays a role analogous to the Arginine finger of the Ras‐RasGAP system, to accelerate otherwise slow GTP hydrolysis rates. In these proteins, two conserved asparagines and a ‘K‐loop’ present in switch‐I, were suggested as attributes of GTPases employing a K+‐mediated mechanism. Based on their conservation, a similar mechanism was suggested for TEES family GTPases. Recently, in Dynamin, Fzo1 and RbgA, which also conserve these attributes, a similar mechanism was shown to be operative. Here, we probe K+‐activated GTP hydrolysis in TEES (TrmE‐Era‐EngA‐YihA‐Septin) GTPases – Era, EngB and the two contiguous G‐domains, GD1 and GD2 of YphC (EngA homologue) – and also in HflX, another GTPase that also conserves the same attributes. While GD1‐YphC and Era exhibit a K+‐mediated activation of GTP hydrolysis, surprisingly GD2‐YphC, EngB and HflX do not. Therefore, the attributes identified thus far, do not necessarily predict a K+‐mechanism in GTPases and hence warrant extensive structural investigations.