Sequence alignments. (a) Alignment detail of YfhM group bacterial α2-macroglobulin sequences from bacterial proteomes plus human α2-macroglobulin (α2M), centred on the conserved CxEQ thioester motif. (b) Alignment of selected bacterial α2-macroglobulin signal peptides possessing the conserved cysteine (C) residue. Signal peptides require a run of hydrophobic residues preceded by a positively charged residue. Cleavage is at the small (glycine (G)/alanine (A)) residue terminating the signal peptide (marked by a dot). Aminoacylation of lipoproteins occurs in the inner membrane at a C (marked by *) directly following the signal peptide. An aspartate residue (D) after the C acts as a retention signal to the inner membrane in E. coli, preventing lipoprotein transfer to the outer membrane [17, 18]. Alignments are color-coded using the Clustal X defaults . Blue denotes conserved hydrophobicity, as in the signal peptide, while a strongly conserved C is colored pink. Accession numbers are SWISS-PROT or NCBI genomes (NP, finished genome; ZP, provisional assignment in unfinished genome). Species names follow the SWISS-PROT convention.