Is the bacteriophage lambda lysozyme an evolutionary link or a hybrid between the C and V-type lysozymes? Homology analysis and detection of the catalytic amino acid residues.

The relationship between the bacteriophage lambda lysozyme (lambda L) and the C and V-type lysozymes has been investigated by sequence alignment, secondary structure prediction and pattern recognition methods. The alignment of the amino terminal part of lambda L with that of V-type lysozymes suggests that Glu19 is a residue essential for catalysis. Its mutation to Gln leads to a completely inactive enzyme. In the alignment of the sequence of lambda L with those of the C-type lysozymes a strongly homologous fragment of about 30 amino acid residues is detected. Taking into consideration this observation and the published structural alignments between C and V-type lysozymes, a repetition of the beta-sheet motif in lambda L is proposed. The multiple alignment draws the attention to a possible catalytic role for Asp34 that would be positioned in the middle of the second strand of the beta-sheet as in the C-type lysozymes. This role is confirmed by mutagenesis. The implications of these observations in terms of the evolutionary relationship between lambda L and the other lysozymes is discussed.