Mutation, Selection, and Functional Repair in Formyl Peptide Receptor Genes: A View on the Selection Processes Occurring in This Gene Subfamily

Abstract

Formyl peptides (FPs) released by some bacteria are powerful chemoattractants and activators of granulocytes, monocytes, and macrophages, acting through the members of a subfamily of specific seven-transmembrane G-protein-coupled formyl peptide receptors (FPRs), which are expressed only in mammals. Upon stimulation, granulocytes chemotactically move towards sites of maximal FP concentration, and release different bactericidal lytic enzymes and reactive oxygen species (ROI). In some instances, such as ischemia/reperfusion, the proinflammatory mediators released by the injured tissues and the intestinal bacteria and endotoxins, which may permeate across the damaged mucosal barrier, prime the inflowing granulocytes for an enhanced ROI production, resulting in severe damage to the host tissues. In this investigation 16 representative FPR and FPR-like mRNAs were selected to study the pattern of mutation/conservation of the individual nucleotides (nt) in the coding sequences. Mutations occur in 56.7%, 46.4%, and 87.5 % of cases in the first, second, and third nt, respectively, of the coding triplets. A probabilistic analysis demonstrated a significant nonrandom linkage between mutations in the first and second nt. Furthermore, the triplets that are variously double-mutated in the first two nt code, on average, for more hydrophobic amino acids (AA) in the transmembrane segments and more hydrophilic AA in the external and intracytoplasmic segments, thus preserving the general structure of the receptor. The authors hypothesize that when in one of the first two nt a mutation leading to a nonfunctioning protein product occurred, the mutated gene was eventually eliminated; however, a second mutation occurring in the other previously unmutated Address correspondence to V. Mitolo, Immunopharmacology and Immunotoxicology Downloaded from informahealthcare.com by University of Waterloo on 11/29/14For personal use only. M.A. Panaro et al.nt may have led to a protein product that is compatible with functional activity, although mutated in one (noncritical) AA. Such double mutations effecting a "functional repair" have thus survived and are retained among the extant sequences. Moreover, the combined mutation of all three nt in coding triplets occurs with a significantly higher than random frequency and this finding may be interpreted in a similar way.

Mutation Patterns in the Chemokine CXC Receptor 4 Gene Subfamily

“…Both characteristics are also present in the mRNAs for N-formyl peptide gene receptors of mammals, (27) as well as in other sequences which were occasionally studied (e.g., the ATP-binding cassette genes of different species from insects to mammals; unpublished). Theoretically, the probability of mutation of the individual nt is the same; however, natural selection will allow the persistence of only those mutations which do not alter the structural/functional characteristics of the molecule, including, among others, the hydrophobicity/hydrophilicity characteristics of some critical aa.…”

“…In (27) we illustrated the possibility that a second mutation, in another element of a triplet, could restore the hydrophobic (or hydrophilic) character of an aa after a first mutation had changed the relevant aa from hydrophobic to hydrophilic (or vice-versa). The present observations (a) and (b) prompted us to study in more detail the effects of single and double mutations in a triplet, with reference to the hydrophobicity index of the corresponding aa.…”

“…The mathematical demonstration of this autocorrelation pattern has been given in . (27) In brief, the negative correlation for lags 1, 4, 7, 10, . .…”

“…(27) It would be of interest to investigate whether similar selection mechanisms, favoring a higher conservation of the second nt and a mutation/conservation linkage (association) between the two first nt, have a more general impact in gene evolution.…”

Mutation, Selection and the Amino Acid Hydropathic Character: A Study on Receptor Genes Involved in Immune and Non-Immune Functions

“…While studying the conservation/mutation patterns of the mRNA sections coding for the N-formyl peptide receptors (in mammals) [1] and the chemokine CXC receptor 4 (in different species) [2] we observed two remarkable characteristics present in both gene subfamilies: (a) on average the second nucleotide (nt) of the coding triplets is better conserved than the first nucleotide (the third nt being, as expected, the least well conserved); and (b) in each triplet the conservation levels of the first and second nt exhibit positive correlation values which are significantly higher than the correlations between the other nt, i.e., first-third and secondthird. The hypothesis that the higher correlation first-second is determined by the strict proximity of the two nt (and thence a very similar exposure to mutagenic agents) may be ruled out since the correlation second-third is significantly lower.…”