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Hhv capsid portal protein

The meaning of «hhv capsid portal protein»

HHV Capsid Portal Protein, or HSV-1 UL-6 protein, is the protein which forms a cylindrical portal in the capsid of Herpes simplex virus (HSV-1). The protein is commonly referred to as the HSV-1 UL-6 protein because it is the transcription product of Herpes gene UL-6.

The Herpes viral DNA enters and exits the capsid via the capsid portal. The capsid portal is formed by twelve copies of portal protein arranged as a ring; the proteins contain a leucine zipper sequence of amino acids which allow them to adhere to each other.[1] Each icosahedral capsid contains a single portal, located in one vertex.[2][3]

The portal is formed during initial capsid assembly and interacts with scaffolding proteins that construct the procapsid.[4] [5] [6] When the capsid is nearly complete, the viral DNA enters the capsid (i.e., the DNA is encapsidated) by a mechanism involving the portal and a DNA-binding protein complex similar to bacteriophage terminase.[7] Multiple studies suggest an evolutionary relationship between Capsid Portal Protein and bacteriophage portal proteins.[2][7]

When a virus infects a cell, it is necessary for the viral DNA to be released from the capsid. The Herpes virus DNA exits through the capsid portal.[8]

The genetic sequence of HSV-1 gene UL-6 is conserved across the family Herpesviridae and this family of genes is known as the "Herpesvirus UL6-like" gene family.[9] "UL-6" is nomenclature meaning that the protein is genetically encoded by the sixth (6th) open reading frame found in the viral genome segment named "Unique-Long (UL)".

Research performed in 2004 used electron microscopy to predict that UL-6 forms 11, 12, 13, and 14-unit polymers. The dodecameric form was found to be most likely.[2]

Refinements to the electron microscopy in 2007 allowed finding that the portal is a twelve (12)-unit polymer present at one of the twelve capsid vertices instead of the UL-19 pentamer found at non-portal vertices.[1]

A study using deletion and mutation of the UL-6 amino acid sequence demonstrated the leucine residues in a predicted leucine zipper motif were required for formation of the dodecameric ring structure.[3]

Assembly of portal units is an initial step in constructing capsids of viral progeny. Capsids assembled in the absence of portals lack portals.[4]

In 2003, gel eletrophoresis studies demonstrated that intact UL-6 portals associate in vitro with viral protein UL-26. This association is antagonized by that action of WAY-150138, a thiourea inhibitor of HHV encapsidation.[5]

Further investigation during 2006 showed that assembly of capsid with portal depends on interaction of UL-6 with "scaffolding" protein UL-26.5, amino acids 143 through 151.[6]

UL-6 associates with a UL-15/UL-28 protein complex during capsid assembly. The UL-15/UL-28 is believed to bind with viral DNA and serve the same purpose as terminase by packing viral DNA into the capsid during capsid assembly.[7]

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