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Mapping the pinhole formation pathway of S 21
Author(s) -
Pang Ting,
Park Taehyun,
Young Ry
Publication year - 2010
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2010.07362.x
Subject(s) - periplasmic space , biology , dimer , membrane , transmembrane domain , biophysics , membrane protein , microbiology and biotechnology , biochemistry , chemistry , escherichia coli , gene , organic chemistry
Summary Phage holins are small, lethal membrane proteins of two general types: canonical holins, like λ S105, which oligomerizes and forms large membrane holes of unprecedented size; and pinholins, like S 21 68 of lambdoid phage 21, which forms homo‐heptameric channels, or pinholes, with a lumen of < 2 nm. Pinholes depolarize the membrane, leading to activation of secreted endolysins and murein degradation. S 21 68 has two transmembrane domains, TMD1 and TMD2. TMD2 alone lines the pinhole, making heterotypic interactions involving two surfaces, A and B. Mutational analysis on S 21 68 suggested that S 21 68 initially forms inactive dimer, with TMD1 inhibiting TMD2 both in cis and trans . When TMD1 exits the membrane to the periplasm, it liberates TMD2 to participate in the pathway to pinhole formation. In this study, further mutational analysis suggests a refined pinhole formation pathway, with the existence of at least two intermediate states. We propose that the pathway begins in the activated dimer state, with a homotypic TMD2 interface involving the A surface. Evidence is presented for a further oligomeric state involving a heterotypic A:B interaction. Moreover, the data suggest that a glycine‐zipper motif present in the A interface of TMD2 is involved in every stage downstream of the inactive dimer.