THE TUBULIN-LIKE S1 PROTEIN OF SPIROCHAETA IS A MEMBER OF THE HSP65 STRESS PROTEIN FAMILY

A 65-kDa protein (called S1) from Spirochaeta bajacaliforniensis was i dentified as 'tubulin-like' because it crossreacted with at least four different antisera raised against tubulin and was isolated, with a co -polymerizing 45-kDa protein, by warm-cold cycling procedures used to purify tubulin from mammalian brain. Furthermore, at least three gener a of non-cultivable symbiotic spirochetes (Pillotina, Diplocalyx, and Hollandina) that contain conspicuous 24-nm cytoplasmic tubules display ed a strong fluorescence in situ when treated with polyclonal antisera raised against tubulin. Here we summarize results that lead to the co nclusion that this 65-kDa protein has no homology to tubulin. SI is an hsp65 stress protein homologue. Hsp65 is a highly immunogenic family of hsp60 proteins which includes the 65-kDa antigens of Mycobacterium tuberculosis (an active component of Freund's complete adjuvant), Borr elia, Treponema, Chlamydia, Legionella, and Salmonella. The hsp60s, al so known as chaperonins, include E. coil GroEL, mitochondrial and chlo roplast chaperonins, the pea aphid 'symbionin' and many other proteins involved in protein folding and the stress response.