PMID:19881499

Citation	Sun, Q, Kuty, GF, Arockiasamy, A, Xu, M, Young, R and Sacchettini, JC (2009) Regulation of a muralytic enzyme by dynamic membrane topology. Nat. Struct. Mol. Biol. 16:1192-4
Abstract	R(21), the lysozyme of coliphage 21, has an N-terminal signal-anchor-release (SAR) domain that directs its secretion in a membrane-tethered, inactive form and then its release and activation in the periplasm. Both genetic and crystallographic studies show that the SAR domain, once extracted from the bilayer, refolds into the body of the enzyme and effects muralytic activation by repositioning one residue of the canonical lysozyme catalytic triad.
Links	PubMed PMC3075974 Online version:10.1038/nsmb.1681
Keywords	Bacteriophage P1/metabolism; Coliphages/metabolism; Muramidase/chemistry; Muramidase/metabolism; Protein Structure, Secondary; Protein Structure, Tertiary; Viral Proteins/chemistry; Viral Proteins/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BPP21:LYS		GO:0003796: lysozyme activity	ECO:0000315:		F		Supplementary Figure 2. is a graph of results of an assay to determine lysozyme activity between purified full-length R^21 and truncated R^21. The truncated version has had the N-terminal SAR (signal anchor release) domain cleaved. Lyz^P1, a protein from phage P1 that had been previously determined to have lyzosyme activity, was included for comparison. The results found that the truncated version of R^21 did not produce any lysozyme activity, while the full-length version produced activity similar to Lyz^P1. The assay was done with the EnzChek® Lysozyme Assay which measures lysozyme activity on fluorescently-labeled Micrococcus lysodeikticus cell walls. When the fluorescently-labeled Micrococcus lysodeikticus cell walls are hydrolyzed, the fluorescein was released from the cell wall resulting in an increase in fluorescence. Trials with different concentrations of egg white lysozyme (EWL) (a standard for the EnzChek test) were run. The different shapes in the graph indicate EWL concentrations. Different line colors indicate which protein was being tested. In each trial, the full-length version of R^21 produced similar activity to Lyz^P1, while the truncated version of R^21 experienced almost total loss of function. These results support the idea that the SAR domain is necessary for and contributes to lysozyme activity in R^21.	complete CACAO 12587
BPP21:LYS	Contributes to	GO:0003796: lysozyme activity	ECO:0000247:	UniProtKB:Q37875	F		Figure 1a is a sequence alignment between R^21 Lyz^P1. Lyz^P1 is a previously researched protein that has lysozyme activity. The orange boxes have been identified as SAR domains, and in supplementary figure 2a are assayed to show the SAR domains are necessary for lysozyme activity. The yellow boxes are amino acid sequences that are inserted to produce chimeras for other tests. Alignment is inferred based on the E-8aa-(D/C)-5aa-T catalytic triad (blue and asterisks).	complete CACAO 12645

References

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