Homologies in the Structures of G-Binding Proteins: An Analysis Based on Elongation Factor EF-TU

Abstract

The defining property of G binding proteins is their ability to bind guanine nucleotides, and in this review we shall concentrate upon the domain or subunit responsible for carrying out this function. A common function of such a general nature, exercised in so many different biological organisms and biochemical contexts, does not automatically imply a high, or even a detectable, degree of homology among the proteins that proffer it. The G-proteins provide a spectrum of degrees of kinship that range from the intimate to the unrecognisable. Satisfyingly, this spectrum correlates largely with similarity of function, at least within the general classes of G-proteins. Nevertheless, among these classes it remains a matter for conjecture whether the difference between just detectable homology and no detectable homology, significant as it may be in the statistical sense, is significant in the subjective sense of “telling us anything about evolution.”