MEMBERS OF THE IMMUNOGLOBULIN SUPERFAMILY IN BACTERIA

We report a prediction that two prokaryotic proteins contain immunoglo bulin superfamily domains. Immunoglobulin-like folds have been identif ied previously in prokaryotic proteins, but these share no recognizabl e sequence similarity with eukaryotic immunoglobulin superfamily (IgSF ) folds, and may be the result of the physics and chemistry of protein s favoring certain common folds. In contrast, the prokaryotic proteins identified have sequences whose match to the immunoglobulin superfami ly can be detected by hidden Markov modeling, BLASTP matches, key resi due analysis, and secondary structure predictions. We propose that the se prokaryotic immunoglobulin-like domains are almost certain to be re lated by divergence from a common ancestor to eukaryotic immunoglobuli n superfamily domains.