Abstract
The alyA gene, encoding a secreted guluronate-specific alginate lyase (Aly) from Klebsiella pneumoniae subsp. aerogenes type 25, has been cloned. DNA sequence analysis reveals two possible translation start sites for the precursor form of Aly and a long open reading frame (ORF) predicted to encode a 287-amino-acid (aa) mature form of Aly, in agreement with N-terminal aa sequence analysis of the protein. Aly has a calculated molecular mass of 31.4 kDa, in good agreement with SDS-PAGE analysis, and a calculated p I of 9.39. Comparison of the deduced aa sequence with a mannuronate-specific lyase from a marine bacterium reveals 19.3% identity and 28.8% similarity with a 9-aa conserved region close to the C terminus, probably of functional or structural significance. There is no obvious sequence similarity with pectate lyases which also catalyse a β-elimination reaction. Heterologous expression of K. pneumoniae alyA in Escherichia coli yields 10 mg of Aly per litre of culture supernatant, apparently due to non-specific release from the periplasm.
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