Three of these hypothetical proteins are encoded by a gene cluster (PPA0532-0534), with homologs only in Corynebacterium spp. Three additional secreted Alisertib order proteins (PPA1715, PPA1939, PPA2175) are unique to P. acnes; PPA1715 contains characteristic repeats of the dipeptide proline-threonine (PT), similar to other putative adhesins (discussed below), and PPA1939 was secreted most strongly by all tested

strains. Future work will determine the function of this abundantly secreted protein. Strain-specific secretion of putative adhesions As expected, the secretomes of the type IB strains, KPA and P6, share a higher degree of similarity with each other than with the other three strains tested. Nevertheless, we identified a few prominent differences between KPA and P6: (i) KPA secreted both CAMP4 and CAMP2. By contrast, P6 exclusively

secreted CAMP2; (ii) KPA was the only strain which secreted PPA2141, a protein unique to P. acnes and with MK-2206 no homology to proteins stored in any database. A likely explanation for the KPA-specific expression of the gene encoding PPA2141 is a duplication of a 12 bp repeat within the 5′-end of the gene in strains 266 and P6 (Fig. 3A). This duplication results in the insertion of four amino acids just after the predicted cleavage site of the signal peptide, which potentially alter secretion; (iii) likewise, PPA1880, which also has no existing homology to other proteins but contains characteristic PT repeats (Fig. 3B), was secreted exclusively by P6. Interestingly, PPA1880 possesses a phase variation-like signature – a stretch of guanine residues, located within the putative promoter region. Sequencing of the upstream region of PPA1880 revealed a variable number of guanine residues in the three strains (11 nt in P6, 13 nt in KPA and 15 nt in 266) (Fig. 3C). Changes in the number of guanine

residues alter the length of the spacer region of the putative promoter. Thus, observed differences in spacer lengths – 18 nt in P6 (close to the consensus length), 20 nt in KPA and 23 nt in 266 – may explain why PPA1880 expression is P6-specific. Alternatively, if the guanine tract is assumed to be part of the N-terminus of PPA1880, frameshifts leading to truncated proteins would be introduced in KPA and 266, but not in P6 (additional file 3) Figure 3 Changes Methocarbamol in repetitive sequences involved in strain-specific expression and secretion of putative adhesins of P. acnes. (a) Insertion of a 12 bp repeat in the 5′-end of PPA2141 in P. acnes strains P6 and 266 results in an altered N-terminus. PPA2141 is secreted only by strain KPA. (b) Proline-threonine (PT) repeats at the C-terminus of PPA1880; these repeats are conserved in the indicated P. acnes strains. (c) Changes in the number of guanine residues in the upstream region of PPA1880, resulting in altered sizes of the spacer region of the possible promoter (in green: putative -35 and -10 region of the promoter; in red: predicted start codon).