Signal sequence and alanine-rich region of streptococcal protein antigen A of Streptococcus sobrinus can direct localization of alkaline phosphatase to the periplasm of Escherichia coli

• Published in: FEMS microbiology letters Vol. 184; no. 1; pp. 17 - 21
• Main Authors: Holt, Robert G, Raju, Latha
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2000
• Subjects: Escherichia coli; Protein localization; SpaA protein; Streptococcus sobrinus; Protein localization; SpaA protein; Streptococcus sobrinus
• DOI: 10.1016/S0378-1097(00)00013-6
• ISSN: 0378-1097

Streptococcal protein antigen A (SpaA) of Streptococcus sobrinus is expressed on the surface of cells and extracellularly. Tn phoA which lacks signals for transcription and membrane transport of Escherichia coli alkaline phosphatase was used to analyze the sequences necessary for transport of a SpaA/PhoA fusion protein across the cytoplasmic membrane to the periplasm of E. coli cells. Of 15 alkaline phosphatase-producing isolates analyzed, all were found to localize more than 85% of the SpaA/PhoA hybrid protein to the periplasm of E. coli cells. From DNA sequence analysis, all were found to have Tn phoA inserted into an identical site. The insertion site of Tn phoA was downstream from the coding sequence that generates four tandemly repeated alanine-rich sequences of 82 amino acid residues. These results suggest that in addition to the signal sequence, mature protein sequences containing alanine-rich repeat sequences may play a role in the export of the SpaA protein across a bacterial membrane.