Biology Reference
In-Depth Information
Fig. 1
The 2D peptide structures of a CC chemokine ligand and a chemokine receptor. The
N
and
the
C
denote the amino and carboxyl termini, respectively. The encircled
C
s represent conserved
cysteine residues. The
dashed lines
indicate conserved disulphide bridges.
Grey boxes
indicate
hydrophobic transmembrane alpha helix domains
the host: (a) CC and CXC chemokine genes and (b) G protein-coupled receptors
(GPCR) genes, the majority of which resembles chemokine receptor genes. GPCRs
form a large family of 7-transmembrane receptors (Fig. 1) that include sensory
receptors for sight, smell, and taste as well as receptors for many neurotransmitters,
peptide hormones and chemokines. Chemokines comprise a family of immune
modulatory cytokine peptides. Currently, four classes of chemokines are known.
The classification is based on a conserved structure (Fig. 1) that includes either a
single cysteine (C), a CC motif (Fig. 1), a CXC motif or a CX3C motif. Chemokines
can be released to initiate inflammatory responses by acting as chemoattractant for
infiltrating leukocytes (Glass et al. 2003). They can also stimulate differentiation,
maturation and activation of many types of immune-related cells (Glass et al. 2003).
Two chemokines, CXCL16 and CX3CL-1, were shown to function as adhesion
molecules for leukocytes that are captured from the bloodstream onto the endothe-
lial surface (Haskell et al. 2000; Nakayama et al. 2003). The purpose of this review
is to summarize the (putative) functions of the CC and CXC chemokines (vCKs) as
well as the chemokine-like GPCRs (vGPCRs) that are encoded by CMV.
Evolution of CMV vCK Genes
To date, three vCK genes have been identified in the HCMV genome (Fig. 2), the
CC chemokine-like gene UL128, and the CXC chemokine-like genes UL146 and
UL147. To some extent, these genes are conserved among primate CMVs (Table 1).
UL128-like genes are also present on the genomes of murine CMV (MCMV) and
rat CMV (RCMV), as well as on the genome of human herpesvirus type 6 (HHV-6)
(Table 1). The rodent CMV and HHV-6 species lack UL146- and UL147-like
