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Crosslinking renders bacteriophage HK97 capsid maturation irreversible and effects an essential stabilization

Crosslinking renders bacteriophage HK97 capsid maturation irreversible and effects an essential... In HK97 capsid maturation, structural change (‘expansion’) is accompanied by formation of covalent crosslinks, connecting residue K169 in the ‘E‐loop’ of each subunit with N356 on another subunit. We show by complementation experiments with the K169Y mutant, which cannot crosslink, that crosslinking is an essential function. The precursor Prohead‐II passes through three expansion intermediate (EI) states en route to the end state, Head‐II. We investigated the effects of expansion and crosslinking on stability by differential scanning calorimetry of wild‐type and K169Y capsids. After expansion, the denaturation temperature (Tp) of K169Y capsids is slightly reduced, indicating that their thermal stability is not enhanced, but crosslinking effects a major stabilization (ΔTp, +11°C). EI‐II is the earliest capsid to form crosslinks. Cryo‐electron microscopy shows that for both wild‐type and K169Y EI‐II, most E‐loops are in the ‘up’ position, 30 Å from the nearest N356: thus, crosslinking in EI‐II represents capture of mobile E‐loops in ‘down’ positions. At pH 4, most K169Y capsids remain as EI‐II, whereas wild‐type capsids proceed to EI‐III, suggesting that crosslink formation drives maturation by a Brownian ratchet mechanism. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The EMBO Journal Wiley

Crosslinking renders bacteriophage HK97 capsid maturation irreversible and effects an essential stabilization

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References (47)

Publisher
Wiley
Copyright
Copyright © 2013 Wiley Periodicals, Inc
ISSN
0261-4189
eISSN
1460-2075
DOI
10.1038/sj.emboj.7600613
pmid
15775971
Publisher site
See Article on Publisher Site

Abstract

In HK97 capsid maturation, structural change (‘expansion’) is accompanied by formation of covalent crosslinks, connecting residue K169 in the ‘E‐loop’ of each subunit with N356 on another subunit. We show by complementation experiments with the K169Y mutant, which cannot crosslink, that crosslinking is an essential function. The precursor Prohead‐II passes through three expansion intermediate (EI) states en route to the end state, Head‐II. We investigated the effects of expansion and crosslinking on stability by differential scanning calorimetry of wild‐type and K169Y capsids. After expansion, the denaturation temperature (Tp) of K169Y capsids is slightly reduced, indicating that their thermal stability is not enhanced, but crosslinking effects a major stabilization (ΔTp, +11°C). EI‐II is the earliest capsid to form crosslinks. Cryo‐electron microscopy shows that for both wild‐type and K169Y EI‐II, most E‐loops are in the ‘up’ position, 30 Å from the nearest N356: thus, crosslinking in EI‐II represents capture of mobile E‐loops in ‘down’ positions. At pH 4, most K169Y capsids remain as EI‐II, whereas wild‐type capsids proceed to EI‐III, suggesting that crosslink formation drives maturation by a Brownian ratchet mechanism.

Journal

The EMBO JournalWiley

Published: Jun 6, 2005

Keywords: ; ; ; ;

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