Abstract

Yeast cell flocculation is a common cellular adhesion process which increases the efficiency of yeast cell harvest and recovery in the beer industry and biofuel production. The flocculation involves the binding of exopolysaccharides to the flocculation protein of neighboring cell. It is of great interest to examine the roles of key amino acid residues in modulating polysaccharide binding which regulates the flocculation. In this work, proper mutation sites were identified via alanine scanning mutagenesis incorporated with molecular dynamics simulations of protein-mannobiose complexes based on the crystal structure of flocculation protein Flo1p. Two mutants Q117N and Q117R have been selected out of nine examined mutants, with stronger binding free energies for the mannobiose binding, comparing to the wild type protein. The two mutants also show enhanced binding in the protein-mannotriose complexes which consist of three mannose residues, fulfilling the capacity of the binding site, and can be used to evaluate the binding strength of oligomannose. Hydrogen bonding, conformational stability and shape change were analyzed to help understand the protein-mannotriose interactions. This study also shows a way to alternate oligosaccharide binding to proteins functioning in other biological processes.