The Properties, Structure And Functions Of Lactic Acid Bacteria S-layer Proteins

Surface layer proteins (s-layer proteins) could self-assemble a paracrystalline,two-dimensional, regular and highly porous array. Because of the beneficial functions andspecial self-assembly property, the s-layer proteins of lactic acid bacteria were taken muchattention. In order to offer theoretical basis for the application of s-layer proteins orlactobacilli carrying them in food pharmaceutical industries, some lactobacilli carrying s-layerprotein were selected. Besides, several properties of the proteins were studied as well as therelationship between the proteins and surface properties (such as auto aggregation, surfacehydrophobicity and surface charge) and adhesion of lactobacilli strains in the paper.Two strains, Lactobacillus helveticus fb213and L. acidophilus fb116, carrying s-layerprotein were selected with the positive control L. acidophilus NCFM. The molecular mass ofthree lactobacilli s-layer proteins were44.6kDa,49.7kDa and46.0kDa, respectively. Andthe protein contents were separately11.7%,13.4%and12.3%. By circular dichroism spectraand LC-MS, the second structure and composition of amino acid of three s-layer proteinswere found similar. The Tmdetermined by DSC were63.67±0.28℃,59.78±0.85℃and61.98±0.67℃, respectively. The surface hydrophobicity indexes analyzed by fluorescencelabeling technology were2.07±0.06,30.47±0.94and7.25±0.13, respectively.Successfully survival in the gastrointestinal tract is an important precondition forpotential probiotics. It was shown that after removing s-layer proteins, the survival of L.acidophilus NCFM, L. helveticus fb213and L. acidophilus fb116in simulated gastric andintestinal juice decreased by2-3log compared with the intact cells. Under the bile level of0.5g/L, the concentrations of s-layer proteins were increased by2.3,2.0and2.5times,respectively, with forming a thicker and harder barrier to resist the invasion of bile. It wasindicated that three s-layer proteins were advantageous barriers for the survival of lactobacilliin the gastrointestinal tract.The surface properties of L. acidophilus NCFM, L. helveticus fb213and L. acidophilusfb116were affected by s-layer proteins. After s-layer protein removing, the auto aggregationof the strains declined10%,20%and21%, respectively. Besides, the surface hydrophobicityof L. acidophilus NCFM rose, and those of L. helveticus fb213and L. acidophilus fb116bothdropped. And the surface charge all decreased. Cell model was built with enterocyte HT29,and the relationship between s-layer proteins and the adhesion of lactobacilli as well as theproteins’ role in inhibition of lactobacilli to the adhesion and invasion of Escherichia coliATCC43893were studied. It was found that s-layer proteins help the adhesion and inhibition.They could be considered as a kind of adhesin, playing a role in the adhesion of threelactobacilli strains and the inhibition to adhesion of E. coli. Thus, they were beneficial to thecolonization of the lactobacilli in gastrointestinal tract.It was concluded that surface properties and adhesion of the two lactobacilli strains wereaffected by their s-layer proteins. Consequently, the lactobacilli exerted health promotingproperties effectively owing to the critical role of the s-layer proteins in strain colonization.