This family consists of uncharacterised bacterial proteins mainly found in Proteobacteria, including YcfL from Escherichia coli and Putative lipoprotein from Campylobacter jejuni. This protein adopts a single domain configuration with two beta-sheets formed respectively by three and four beta-strands (beta-sandwich) and contains a Greek key motif, representing a singular variant of the Ig-like fold. Many proteins of this group have a lipid attachment site at the N-terminal of this domain, which together with the structure solved, suggests a role in bacterial lipoproteins [1].

1: Crystal structure of the Campylobacter jejuni Cj0090 protein reveals a novel variant of the immunoglobulin fold among bacterial lipoproteins. Paek S, Kawai F, Choi KJ, Yeo HJ; Proteins. 2012;80:2804-2809. PMID:22987763