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valence 736 varicella
valence
The number of antigen-binding sites on an antibody molecule
or the number of antibody-binding sites on an antigen
molecule. The valence equals the maximum number of
antigen molecules that can combine with a single antibody
molecule. Antigens are usually multivalent; most antibodies
are bivalent. Immunoglobulin M (IgM) has a valence as
high as 10. The valence of IgA differs depending on its level
of polymerization. Antibodies of the IgG, IgD, and IgE
classes have valences of 2. Due to steric hindrance, antibodies
usually bind less antigen than would be expected based
on valence. Antibody molecules are bivalent or multivalent;
T lymphocyte receptors are univalent.
Hydrogen
bonding
O
H
O
Before dipole
forms
After dipole
forms
– +
– +
Electrostatic
force
–
+
van der Waals forces.
Antibody affinity.
Vander
Waals
force
– +
+
–
Hydrophobic
force
Attractive forces binding antigen to antibody.
H 2 O
excluded
van der Waals forces
Weak forces of attraction among atoms, ions, and molecules.
It is active only at short distances and varies inversely to the
seventh power of the distance between ions or molecules.
Thus, van der Waals forces may be important in antigen–
antibody binding. A consequence of oscillation of polarities
in the outer electron clouds of two nearby atoms, leading to
the formation of attractive/repulsive forces between them.
variability plot
Refer to Wu–Kabat plot.
variable (V) domain
An Ig or TCR chain N terminal domain encoded by the corresponding
variable (V) exon. The variable domains of Ig
heavy and light chains and TCR-α and -β chains characterize
the variable regions and antigen-binding sites of Ig and TCR
molecules. Paired amino terminal variable domains of Ig
and T cell receptor polypeptide chains constitute the antigenbinding
site.
variable (V) exon
Gene coding sequence for the variable domain of an Ig or
TCR protein. The Igk, Igl, TCR-α and TCR-δ loci V exons
are assembled randomly from V and J gene segments,
whereas the Igh, TCR-β and TCR-γ are comprised of V, D
and J gene segments.
variable (V) gene segment
The immunoglobulin or T cell receptor gene DNA sequence
that encodes the V domain’s approximately first 95 amino
acids. The germline genome contains numerous different V
gene segments. To construct a complete exon that encodes a
V domain, it is necessary to rearrange one V gene segment
to link with a J or a rearranged DJ gene segment.
variable lymphocyte receptors (VLRs)
GPI-anchored cell surface receptors expressed by primitive
Agnatha lymphocytes. They undergo somatic variation.
variable (V) region
The part of an immunoglobulin molecule or T cell receptor
in the N terminal portion of its constituent polypeptide
chains that reveal a high level of amino acid variability and
defines antigen recognition. Isoforms with different antigen
specificities vary in amino acid sequence. The segment of
an immunoglobulin molecule or antibody formed by the
variable domain of a light polypeptide (κ or λ) or heavy
polypeptide (α, γ, μ, δ, or ε) chain, sometimes called the Fv
region, and encoded by the V gene. This region of the molecule
is responsible for the specificity of the antigen bound.
The antigen-binding variable sequences are present in the
extended loop structures or hypervariable segments. Refer
also to the variable region (V) of T cell receptor α, β, γ, and
δ chains that contain variable amino acid sequences.
variable surface glycoproteins (VSGs)
Surface coat constituents of African trypanosomes. By a
process similar to gene conversion, a trypanosome may
alter its surface glycoprotein coat by expressing different
glycoprotein genes.
varicella
A human herpesvirus type 3 (HHV-3) induced in acute
infection, usually occurring in children below 10 years of
age. Anorexia, malaise, low fever, and a prodromal rash follow
a 2-week incubation. Erythematous and pruritic papules
appear in crops and intensify for 3 to 4 days. Complications
include viral pneumonia, secondary bacterial infection,
myocarditis, thrombocytopenia, glomerulonephritis, and