Cloning and characterisation of malE in Burkholderia pseudomallei

No recombinant protein is available for serodiagnosis or skin test in the d iagnosis of melioidosis, This report describes the cloning of the malE gene , which encodes an immunogenic protein of Burkholderia pseudomallei. Bi-dir ectional DNA sequencing of malE revealed that the gene contained a single o pen reading frame encoding 416 amino acid residues with a predicted molecul ar mass of 44.4 kDa. BLAST analysis showed that the putative protein encode d by malE is homologous to the maltose-binding protein (MBP) of other bacte ria. It has 48% and 63% amino acid identity and similarity with the MBP of Brucella abortus, and malE complementation assay showed that it partially c omplemented the function of the MBP of Escherichia coli, Several highly con served regions among the MBP of B. pseudomallei, Br. abortus, Salmonella en terica serotype Typhimurium, E. coli and Enterobacter aerogenes were observ ed, These regions represent signatures A, B, C, D and F identified in the M BP of E, coli, Further sequence analysis revealed that the first 24 amino a cid residues of the MBP of B, pseudomallei probably represent the N-termina l signal peptide of the protein. Similar to the signal peptide of the MBP o f E, coli, Ent, aerogenes and S. Typhimurium, the MBP of B, pseudomallei co ntains two basic residues in the first eight amino acids, followed by a hyd rophobic core, with the last three amino acids in the signal peptide being Ala-Gln-Ala, conforming to the consensus sequence Ala-X-Ala at positions -3 to -1 relative to the site of proteolytic cleavage for recognition by sign al peptidase I, Further studies on serodiagnosis of melioidosis with recomb inant MBP should be performed.