The DUF322 protein Asp23 of Staphylococcus aureus is membrane localized and functionally linked to cell wall stress. Staphylococcus aureus

With a copy number of about 25,000 molecules per cell, Asp23 is one of the most abundant proteins in Staphylococcus aureus. Asp23 has been characterized as a protein with an apparent molecular mass of 23 kDa that, following an alkaline shock, accumulates in the soluble protein fraction. Moreover, it was shown that transcription of the asp23 gene is exclusively regulated by the alternative sigma factor B. The function of Asp23, however, has remained elusive. Sequence analysis identified Asp23 as a Pfam domain of unknown function 322 (DUF322) family member, precluding functional predictions based on its sequence. Using fluorescence microscopy we found that Asp23 colocalizes with the staphylococcal cell membrane. Interestingly, Asp23 appeared to be excluded from sites of active cell division. We identified SAOUHSC_02443 as Asp23 membrane anchor and renamed it as AmaP (Asp23 membrane anchoring protein). To gain evidence for the function of Asp23, a deletion mutant was constructed and a comparative analysis of the wild type and mutant transcriptome was carried out. This analysis identified genes of the cell wall stress stimulon as up regulated in the asp23 mutant. Furthermore, using transmission electron microscopy of negatively stained Asp23 protein we showed that it forms large, highly flexible spiral-like complexes in vitro. In summary, we identified Asp23 as a membrane associated protein in S. aureus that forms large, elongated complexes in vitro and suggest a function for Asp23 in cell envelope homoeostasis. Overall design: Sample versus pool design, pool = mixture of equal amounts of all sample RNAs analyzed, all RNAs (every strain and time point) were isolated as biological triplicates