HHV Capsid Portal Protein, or HSV-1 U
L-6 protein, is the
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
which forms a cylindrical portal in the
capsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
of
Herpes simplex virus (HSV-1). The protein is commonly referred to as the ''HSV-1 U
L-6'' protein because it is the
transcription product of Herpes
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
U
L-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
A leucine zipper (or leucine scissors) is a common three-dimensional structural motif in proteins. They were first described by Landschulz and collaborators in 1988 when they found that an enhancer binding protein had a very characteristic 30-amin ...
sequence of
amino acids
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
which allow them to adhere to each other.
[
] Each
icosahedral
In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons".
There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...
capsid contains a single portal, located in one vertex.
[(Article]
[
]
The portal is formed during initial capsid assembly and interacts with ''scaffolding proteins'' that construct the procapsid.
[
]
[
(Article]
[
] 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
A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...
terminase.
[
] Multiple studies suggest an
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary relationship between Capsid Portal Protein and bacteriophage portal proteins.
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.
[
]
The genetic sequence of HSV-1 gene U
L-6 is conserved across the family
Herpesviridae
''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπει ...
and this family of genes is known as the "Herpesvirus UL6-like" gene family.
[Herpesvirus UL6 like Conserved Domains view at NCBI](_blank)
/ref> "UL-6" is nomenclature
Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal naming conventions, conventions of everyday speech to the i ...
meaning that the protein is genetically
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar working i ...
encoded by the sixth (6th) open reading frame
In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readin ...
found in the viral genome segment named "Unique-Long (UL)".
Studies
Dodecameric structure
Research performed in 2004 used electron microscopy
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
to predict that UL-6 forms 11, 12, 13, and 14-unit polymers. The dodecameric form was found to be most likely.
Leucine zipper creates inter-protein adhesion
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.
Early involvement in capsid assembly
Assembly of portal units is an initial step in constructing capsids of viral progeny. Capsids assembled in the absence of portals lack portals.
Interaction with capsid scaffolding protein
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
Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the ''thio-'' prefix); however, the properties of urea ...
inhibitor of HHV