Hsp70s Contain a Specific Sulfogalactolipid Binding Site. Differential Aglycone Influence on Sulfogalactosyl Ceramide Binding by Recombinant Prokaryotic and Eukaryotic Hsp70 Family Members

Specific 3‘-sulfogalactolipid [SGL-sulfogalactosyl ceramide (SGCer) and sulfogalactosylglycerolipid (SGG)] binding is compared for hsp70s cloned from Helicobacter pylori, Haemophilus influenzae, Chlamydia trachomatis serovar E, Escherichia coli, murine male germ cells, and the hsp70-like extracellular domain within the sperm receptor from Strongylocentrotus purpuratus. This lectin activity, conserved among the different hsp70 family members, is modulated by the SGL aglycone. This is shown by differential binding to both SGC fatty acid homologues and 3‘-sulfogalactolipid neoglycoproteins generated by coupling bovine serum albumin (BSA) and glycosyl ceramide acids synthesized by oxidation of the double bond of sphingosine. Eukaryotic hsp70s preferentially bound the SGCer fatty acid homologues SG24Cer, SG18Cer, and SG20:OHCer, while prokaryotic hsp70s bound SG18:1Cer and SG20:OHCer. Eukaryotic hsp70s bound SGCer−BSA and SG24Cer−BSA conjugates where the latter is the main constituent in SGCer−BSA, while prokaryotic hsp70s bound SG20:OHCer−BSA. None of the hsp70s bound sulfogalactosyl sphingosine (SGSph) or SGSph−BSA, further demonstrating the important role of the aglycone. Although the primary SGL recognition domain of all hsp70s is conserved, we propose that aglycone organization differentially influences the interaction with the sub-site. Heterogeneous SGCer aglycone isoforms in cells and the differential in vitro binding of eukaryotic and prokaryotic hsp70s may relate to their different adhesin roles in vivo as mediators of germ cell and bacterial/host interactions, respectively.