Topologically Linked Protein Rings in the Bacteriaphage HK97
Capsid
Source: Science,Vol289;2129-2133 (22 September
2000)
Authors: William R. Wikoff, Lars Lilias, Robert
L. Duda, Hiro Tsuruta, Roger W. Hendrix,
John E Johnson
Speaker: LS 02 ¥]²±¬Õ u871603
Abstract:
Topological links, or catenanes, are an uncommon
feature of molecular architecture. Protein catenanes, in which a link would
be formed by one covalently bonded protein subunit, was not found before.
The first example found of protein catenanes is the double-stranded DNA (dsDNA)
bacteriophage HK97 capsid. HK97 gp5, a new category of virus fold, has no
structural similarity to any previously determined capsid protein. In the
final maturation step of HK97 an autocatalytic reaction that creats 420 isopeptide
bonds between proteins take place. As a results, there are 60 hexamerric and
12 pentameric rings of covalently joined subunits loopig through each other,
forming a protein chainmail. This chainmail, or protein catenanes, provide
a stabilization mechanism for the very thin HK97 capsid and increase in the
evolutionary advantage. 