A three base pair deletion encoding the amino acid (lysine-270)in the α-cone transducin gene

[摘要] Purpose: Cone transducin plays an important role in interacting withthe cone photoreceptor visual pigments and activating the cGMP-dependentphosphodiesterase. The human gene for the α-subunit of conetransducin (GNAT2) has been cloned and characterized. Recentlyachromatopsia has been associated with mutations in this gene. Cone andcone-rod dystrophies are a genetically heterogeneous group ofphotoreceptor diseases, in which mutations of a single gene may cause avariety of phenotypes. In this study we tested the hypothesis thatmutations in GNAT2 cause cone-rod degeneration (CRD).Methods: PCR-SSCP and heteroduplex analysis combined with automatedsequencing was used for mutation detection in GNAT2 in 13independent pedigrees with CRD. We used co-segregation analysis toestablish or reject causation, when possible. Molecular computermodeling was utilized to examine the possible consequences of mutationsonto GNAT2 protein structure.Results: We found a novel 3 base-pair deletion, predicted to causethe loss of a highly conserved lysine at position 270 (K270del) in aFrench-Canadian CRD pedigree. We detected this deletion in a CRDproband, but also in his unaffected son, the proband's unaffected fatherand the proband's unaffected brother. However, we did not find thisdefect in 12 other CRD pedigrees, nor in 100 normal, culturally matchedchromosomes. According to literature and our molecular computermodeling, the K270 plays an important role in securing the guanine ringin the nucleotide binding cleft of the molecule and in creating a saltbridge between the helical and GTPase domains of GNAT2. However, theK270del in GNAT2 does not appear to have extensive consequences to thestructure and the function of the GNAT2. Apparently, there is acompensatory effect of lysine (K-271), which forms a hydrogen bond withthe N1 ring nitrogen substituting for the loss of the lysine at position270.Conclusions: We detected a deletion of a highly conserved lysine atcodon 270 in a critical functional area of the α-cone transducinmolecule. The co-segregation analysis showed that the deletion is notco-inherited with the disease phenotype and therefore is not the diseasecausing mutation. Apparently the function of this molecule is notaltered by this mutation, due to a compensatory effect of aminoacid 271.Taken together, the presence of this deletion in healthy individuals,and our protein modeling results, predict that α-cone transducinmolecule is able to tolerate structurally and functionally the K270del.

[学科分类] 生物化学/生物物理