title: Evolution of hemopoietic ligands and their receptors. Influence of positive selection on correlated replacements throughout ligand and receptor proteins.
abstract: The rates of amino acid replacement in cytokines and their receptors are high and vary considerably. To determine whether this reflects the action of positive selection, rates of nonsynonymous DNA substitution were examined and found to exceed the synonymous substitution rate in certain exons of rodent IL-3, granulocyte-macrophage stimulating factor, and IL-4. To determine the extent to which positive selection could account for correlations between the amino acid replacement rates of hemopoietins and their receptors, rates were examined in various domains: the correlation with ligand rate was not confined to the ligand-binding domain of the receptor, but extended into the transmembrane and cytoplasmic domains and even to leader peptide domains of both ligand and receptor. As the majority of these replacements are unlikely to be strongly advantageous, different levels of both positive and purifying selection contribute to the extensive variation in hemopoietin/receptor evolutionary rates. Changes in a few residues critical for ligand-receptor interaction may be followed by changes of lesser selective importance in both molecules: replacements of growth hormone residues that form hydrogen or salt bridges with the receptor occur in lineages in which there are many concurrent replacements. A ligand/receptor rate correlation is not found between the seven-transmembrane receptors and their ligands, whose mature forms are often short and completely conserved. This study predicts that a minority of concurrent evolutionary changes in hemopoietins and their receptors reflect directly compensatory changes.
authors.affiliation: Department of Genetics, Trinity College, Dublin, Ireland.
authors.forename: D C
authors.initials: DC
authors.lastname: Shields
authors.forename: D L
authors.initials: DL
authors.lastname: Harmon
authors.forename: A S
authors.initials: AS
authors.lastname: Whitehead
mesh_terms: D000596:Amino Acids / Q000235:genetics; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics; D050822:Cytokine Receptor gp130; D019143:Evolution, Molecular; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000737:chemistry / Q000235:genetics; D016298:Hematopoietic Cell Growth Factors / Q000737:chemistry* / Q000235:genetics*; D006801:Humans; D007377:Interleukin-3 / Q000737:chemistry / Q000235:genetics; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics; D009363:Neoplasm Proteins; D011323:Primates; D011518:Proto-Oncogene Proteins / Q000235:genetics; D018121:Receptors, Cytokine; D017467:Receptors, Erythropoietin / Q000235:genetics; D017978:Receptors, Growth Factor / Q000737:chemistry* / Q000235:genetics*; D015375:Receptors, Interleukin-2 / Q000737:chemistry / Q000235:genetics; D053628:Receptors, Thrombopoietin; D012377:Rodentia; D013926:Thrombopoietin / Q000235:genetics
chemical_list: D000596:Amino Acids; D015703:Antigens, CD; D016298:Hematopoietic Cell Growth Factors; C494199:IL6ST protein, human; D007377:Interleukin-3; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D017467:Receptors, Erythropoietin; D017978:Receptors, Growth Factor; D015375:Receptors, Interleukin-2; D053628:Receptors, Thrombopoietin; D050822:Cytokine Receptor gp130; C082218:MPL protein, human; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D013926:Thrombopoietin