Crystal Structure of Glycoprotein B from Herpes Virus Simplex 1
Glycoprotein B is vital in cell fusion of Herpesvirus. Determination of Crystal structure allows us to find possible avenues into prevention of fusion in turn preventing replication.
Herpes Simplex Virus 1 [HSVto1] is used as a prototype for the large and diverse herpesvirus family. H Glycoprotein B [gB] is vital for viral growth. The precise function of gB is unknown. gB is a 904 residue protein. The crystal structure for the ectodomain of residues Asp103 to Ala730 due to trypsin cleavage used in the sample preparation meaning residues 28 to 102 were missing when protein was crystallized . The crystal structure is refined at 2.1 Angstrom [A] resolution containing three promoters A B and C. Roughly 10% of the polypeptide chain is disordered. In gB there is no real trimerization area but instead multiple promoter contacts throughout the molecule contribute to it’s trimer stability . The 10 cysteines in each subunit form five intra molecular ditosulfide bonds which agrees with structures already determined using mass spectrometry for HSV-2gB . Each promoter is able to be broken into five distinct domains. I; base II; Middle III; Core IV; Crown V;Arm.[Fig .1]
Domain I consists of residues Ile154toVal363 [Fig.1.]. It has a fold which is characteristic of a pleckstrin homology [PH] domain[1,3] and a ?? sandwich composed of two orthogonal ?? sheets composed of four and three strands respectively. Proteins with this particular fold act as a scaffold to accommodate phosphoinositide/peptide binding. In domain I the helix that a PH usually covers is replaced by a long loop and short helix. Inserting residues Tyr165to Ile272 between strands ??4to??11 creating a subdomain consists of a four strand ??sheet. The convex side of the helix is covered with an ?? helix and a ?? hairpin and a short two strand ?? sheet..
Domain II compromises of 2 discontinuous segments Tyr 153toAsn153 and to Cys364toThr 459[Fig.1]. In the centre there is a six strand ?? barrel very similar to the PH superfold with the ??5 of the canonical PH domain absent and in its place a helixtostrand insert on the barrels outer face. All of domain I is placed between strands ??3 and ??17 which are the first and second strands of domain II . Residues 462to477 have recently been ordered and are seen to form a helix ??X in this domain. Residues 477to491 of the promoter regions are still unsolved and are said to be disordered  [Fig.1]. Tryptic cleavage at Arg474 and Lys475 has more than likely destabilized the loop which lies on the edge of domain II and is a target for postransitional cleavage in some strains of herpesvirus such as HCMV .
Domain III comprises of three discontinuous segments which are made up of residues Pro117 to Pro133, Ser 500 to Thr572 and Arg661toThr669. It is composed of a ?? helix 44 residues long which precedes a short helix and a small mixed ?? sheet. These form the central coil of the structure. Arg661toThr669 of the outer ?? strand belong to neighbouring promoter instead of the same polypeptide chain. This region is not a domain but contributes many trimer contacts which are essential .
Domain IV is made up of 2 discontinuous segments residues Ala111toCys116 and Cys573 to Ser660 with di-sulfide bonds linking them C1 to C8. The domain has no similar structural relatives to ones previously described.
Domain V is composed of residues Phe670 to Ala725 and stretches from one end of the molecule to the other as a long extension [Fig.1].Residues in this domain do not come into contact with the rest of the polypeptide chain of the same promoter but instead sits into a groove between the main domains of the other two promoters helping reinforcing trimer interactions.
The crystal structure of gB for Herpesvirus was seen to have five domains per promoter each of which are vital to its function
[Fig.1].A single promoter with domains colored I, pale blue II, pale green III, yellow IV, Orange and V, red. All domains labelled.(3)
 Ekaterina,Heldwein,E et al, Science Mag:,Crystal Structure of Glycoprotein B from Herpes Simplex Virus 1 http://www.sciencemag.org.proxy.lib.ul.ie/content/313/5784/217.full.pdf 
 Weizhong.C,Baohua.G,Stanley.PJournal of Virology:Role of Glycoprotein B of herpes simplex virus type 1 in viral enty and cell fusion
 Stampfer.S,Cohen.G et al,Journal of Virology: Structureal basis of Local, pH-Dependent Conformational Changes in Glycoprotein B from Herpes Simplex Virus Type 1 http://jvi.asm.org/content/84/24/12924.full#ref-18 
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