OBJECTIVETo compare the gene sequence and protein structure of lactate dehydrogenase (LDH) in Streptococcus oligofermentans with those of other bacteria with different acid generating capacities in oral cavity and to analyze the differences of their LDH.

METHODSLDH gene sequence of Streptococcus oligofermentans was measured by Institute of Microbiology, Chinese Academy of Sciences. LDH gene sequences of four Streptococcus and Lactobacillus casei in the NCBI Genbank was identified and compared among the six bacteria's LDH gene sequences and amino acid sequences by BLAST software. ExPASy database was used to predict the physical-chemical characteristics, secondary structure, trans-membrane regions, and spatial structure of Streptococcus oligofermentans LDH protein, which was compared with those of other bacteria.

RESULTSThe full-length of the LDH gene sequences of Streptococcus oligofermentans was 987 base pairs. The highest similarity was 89% with that of the Streptococcus sanguis, and 81% similarity with Streptococcus mutans, and 70% similarity with Lactobacillus casei. LDH amino acid sequence of Streptococcus oligofermentans was similar to Streptococcus sanguinis, with the highest similitude of 96%, with a similitude of 81% to Streptococcus mutans, but differed greatly from that of Lactobacillus casei, with a similitude of only 66%. Streptococcus oligofermentans LDH protein's physical-chemical characteristics, trans-membrane region's numbers, proportions of secondary structure, structural domain's location resembled those of Streptococcus mutans, Streptococcus sanguinis and Lactobacillus casei. Spatial structure differences between the LDH of Streptococcus oligofermentans and that of Streptococcus mutans and Lactobacillus casei were distinct.

CONCLUSIONSStreptococcus oligofermentans LDH's gene sequence, amino acid sequence, and spatial structure all vary from those of Streptococcus mutans and Lactobacillus casei, and these differeces may be a inherent reason that lead to the changes of its LDH's biological functions and incapacity of producing lactic acid.