Sandbox Reserved 717: Difference between revisions

The collar domain is a small globular domain. It contains six beta-strands and an alpha-helix.

For generating the 45kDa fragment the full length gp12 was co-expressed with its chaperone gp57 and purified [1]. Like the 33kDa fragment it also starts with the amino acid Leu85. The 45kDa fragment contains the residues 397-517, which are in the 33kDa fragment internal deleted.

Like the 33kDa fragment the 45kDa fragment can also be divided into two subunits. These two subunits are called head (residues 397-446 and residues 487-517) and bonnet (residues 447-487). On the border between the head and the bonnet subunit there is a metal-binding site.   

Gp12 is fixed with its N-terminal domain to the baseplate. So the C-terminal domain has to be involved in LPS-binding. To detect where the receptor-binding domain is, full-length gp12, 33kDa fragments and 45kDa fragments were immobilised in micro-plate wells and were allowed to bind to bacteria[1]. The result was that the 33kDa fragment did never bind to a bacteria. The 45kDa fragment did bind. So the receptor-binding domain is absent in the 33kDa fragment but present in the 45kDa fragment. The residues which are present in the 45kDa fragment and lacking in the 33kDa fragment are the residues 397-517. They are referred to be part of the receptor-binding domain.

The receptor-binding domain can be sub-divided into head and bonnet. On the border between these two subdomains there is a metal-binding site. This site binds presumably to zinc. Two His amino acids (His445 and His447) from each monomere are octahedrally coordinated around the zinc.  

The exact position of the lipo-polysaccharide(LPS)-binding site is not known. Proteolysis experiments showed, that it contains to the domain with the residues 397-517. Compared with the homologous bacteriophage T4-like strain AR1 sequence, which also binds to the same LPS core molecule like gp12, there can be some possible binding residues be assumed.