Rare lipoprotein A (RlpA) contains a conserved region that has the double-psi beta-barrel (DPBB) fold. The function of RlpA is not well understood, but it has been shown to act as a prc mutant suppressor in Escherichia coli. The DPBB fold is often an enzymatic domain. The members of this family are quite diverse, and if catalytic this family may contain several different functions. Another example of this domain is found in the N-terminus of pollen allergen. Recent studies show that the full-length RlpA protein from Pseudomonas Aeruginosa is an outer membrane protein that is a lytic transglycolase with specificity for peptidoglycan lacking stem peptides. Residue D157 in UniProtKB:Q9X6V6 is critical for lytic activity.