Alignment of Gap3 and its homologues. The black box represents identical or highly conserved residues. The gray box represents similar or less conserved residues. The red arrowed lines indicate the putatively important regions. The red numbers represent the residues chosen for site-directed mutagenesis. Gap3: glycosylation associated protein-3 of S. parasanguinis. Asp3: accessory secretory protein-3 of S. gordonii. SAG1450: hypothetical protein of S. agalactiae. SP1760: hypothetical protein of S. pneumoniae. SE2245: hypothetical protein of Staphylococcus epidermidis. gbs1519: hypothetical protein gbs1519 of S. agalactiae.