A highly selective oligopeptide binding protein from the archaeon Sulfolobus solfataricus

SSO1273 of Sulfolobus solfataricus was identified as cell surface-bound protein by a proteomics approach. Sequence inspection of the genome revealed that the open reading frame of sso1273 is associated in an operon-like structure with genes encoding all the remaining components of a canonical protein-dependent ATP-binding cassette (ABC) transporter. sso1273 gene expression and SSO1273 protein accumulation on the cell surface were demonstrated to be strongly induced by the addition of a peptide mixture (tryptone) to the culture medium. The native protein was obtained in multimeric form, mostly hexameric, under the purification condition used, and it was characterised as an oligopeptide binding protein, named OppASs. OppaASs possesses a typical sequence patterns required for glycosylphosphatidylinositol lipid anchoring and resulted to be N-linked glycoprotein with carbohydrate moieties likely composed of high mannose, and/or hybrid complex carbohydrates. OppASs specifically binds oligopeptides and shows a marked selectivity for amino acid composition of substrates when assayed in complex peptide mixtures. Moreover, a truncated version of OppASs, produced in recombinant form and including the putative binding domain, showed a low but significant oligopeptide binding activity