It has been proposed that proteins which are involved in host defence and s
usceptibility undergo accelerated evolution. Chemokine receptors have roles
as pro-inflammatory agents acting in response to infection: and in additio
n are receptors for entry of viruses and other pathogens into cells. Consis
tent with this, their rate of evolution is higher than that for other membe
rs of the seven-transmembrane domain receptor family. The pattern of evolut
ion of the chemokine receptors was examined in detail. Both chromosomal clu
sters of chemokine receptors (CC and CXC) showed evidence of a number of ge
ne conversions. These are likely to have resulted in protein sequence chang
es, which could possibly alter function. 45% of a control group of clustere
d genes also showed evidence of conversion. Thus, the fixation of a gene co
nversion is not in itself sufficiently unusual in tandemly repeated genes a
nd cannot be taken as strong evidence of a selection for a novel function.
However, the degree of amino acid difference between the chemokine receptor
s CCR1 and CCR3 was greater than that for any of the control genes. Such ch
anges could have functional implications for inter-species differences in c
hemokine receptor interactions with pathogens. (C) 2000 Elsevier Science B.
V. All rights reserved.