Abstract
BackgroundThe salivary mucin MUC7 (previously known as MG2) can adhere to various strains of streptococci that are primary colonizers and predominant microorganisms of the oral cavity. Although there is a growing interest in interaction between oral pathogens and salivary mucins, studies reporting the specific binding sites on the bacteria are rather limited. Identification and characterization of the specific interacting proteins on the bacterial cell surface, termed adhesins, are crucial to further understand host-pathogen interactions.ResultsWe demonstrate here, using purified MUC7 to overlay blots of SDS-extracts of Streptococcus gordonii cell surface proteins, 4 MUC7-binding bands, with apparent molecular masses of 62, 78, 84 and 133 kDa from the Streptococcus gordonii strain, PK488. Putative adhesins were identified by in-gel digestion and subsequent nanoLC-tandem mass spectrometry analysis of resultant peptides. The 62 kDa and 84 kDa bands were identified as elongation factor (EF) Tu and EF-G respectively. The 78 kDa band was a hppA gene product; the 74 kDa oligopeptide-binding lipoprotein. The 133 kDa band contained two proteins; alpha enolase and DNA-directed RNA polymerase, beta' subunit. Some of these proteins, for example alpha enolase are expected to be intracellular, however, flow cytometric analysis confirmed its location on the bacterial surface.ConclusionOur data demonstrated that S. gordonii expressed a number of putative MUC7 recognizing proteins and these contribute to MUC7 mucin binding of this streptococcal strain.
Highlights
The salivary mucin mucin 7 (MUC7) can adhere to various strains of streptococci that are primary colonizers and predominant microorganisms of the oral cavity
Purification of MUC7 A rapid two step chromatographic protocol as described by Mehrotra et al [31] was applied to purify MUC7 from the saliva. This method provided the recovery of this molecule at high purity and in adequate amount (750 g/ml, as assessed by refractive index measurement, data not shown), enabling MUC7-streptococcus binding studies
Purity of the MUC7 preparation was assessed by SDSPAGE, Western blotting and mass spectrometry
Summary
The salivary mucin MUC7 (previously known as MG2) can adhere to various strains of streptococci that are primary colonizers and predominant microorganisms of the oral cavity. Saliva lubricates the oral cavity and contains innate defense related proteins (i.e. cystatins, lysozyme, prolinerich proteins, histatins, lactoperoxidase, lactotransferrin, Poly Ig receptor, DMBT1 and mucins [1,2]) that protect the surfaces of the mouth exposed to the external environment. Mucins are the major macromolecular component of the secretion and human saliva has been shown to contain at least two structurally and functionally distinct populations of mucins: the high molecular weight (Mr > 106 Da) polymeric, gel-forming population, MUC5B, (MG1) and the lower molecular weight (Mr 1.2–1.5 × 105 Da) non-polymerizing population MUC7 (formerly known as MG2) [3,4,5,6]. MUC5B has a much more complex O-glycan profile showing substantial inter-individual variations [10]
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