Identification of a putative sordarin binding site in Candida albicans elongation factor 2 by photoaffinity labeling

Candida albicans EF-2 binds sordarin to a single class of binding sites wit h K-d = 1.26 mum. Equimolar mixtures of EF-2 and ribosomes, in the presence of a non-hydrolyzable GTP analog, reveal two classes of high affinity sord arin binding sites with K-d = 0.7 and 41.5 nm, probably due to the existenc e of two ribosome populations. Photoaffinity labeling of C. albicans EF-2 i n the absence of ribosomes has been performed with [C-14]GM258383, a photoa ctivatable sordarin derivative. Labeling is saturable and can be considered specific, because it can be prevented with another sordarin analog. The fr agment GIn(224)-LYS232 has been identified as the modified peptide within t he EF-2 sequence, Lys(228) being the residue to which the photoprobe was li nked. This fragment is included within the G " -subdomain of EF-2. These re sults are discussed in the light of the high sordarin specificity toward fu ngal systems.