p.G390V Glu390Val (p.G418V Glu418Val in primary sequence with 28 amino-acids signal peptide) also known as F-2 Fluoride-resistant;Fluoride-2 variant/succinylcholine resistance CHE*390V also known as F-2
Kinetic parameters
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References:
Title: Recombinant human butyrylcholinesterase G390V, the fluoride-2 variant, expressed in Chinese hamster ovary cells, is a low affinity variant Masson P, Adkins S, Gouet P, Lockridge O Ref: Journal of Biological Chemistry, 268:14329, 1993 : PubMed
Kinetics of recombinant fluoride-2 variant of human butyrylcholinesterase (Gly390 Val) secreted by Chinese hamster ovary cells were compared to recombinant usual and to usual butyrylcholinesterase purified from human plasma. The usual and fluoride-2 variant were indistinguishable with regard to hydrolysis of benzoylcholine (Km = 5 microM), neutral esters, and at high concentrations of acetylthiocholine, propionylthiocholine, and butyrylthiocholine. However, at low substrate concentrations Km values for acetylthiocholine and succinyldithiocholine were 2-6-fold higher for the fluoride-2 variant. pH rate profiles revealed small differences in pKa that could be attributed to changes in the active site histidine environment. On the other hand, Arrhenius plot analysis of o-nitrophenylbutyrate hydrolysis at pH 7.5 showed no difference in activation energy between fluoride-2 and usual butyrylcholinesterases. Both exhibited an anomalous temperature dependence with a wavelike change in activation energy around 18 degrees C. Affinity of the fluoride-2 variant for sodium fluoride, tacrine, dibucaine, amodiaquin, and succinyldicholine was lower than for usual enzyme. Apparent Ki for succinyldicholine was 125 microM for the fluoride-2 variant and 20 microM for the usual enzyme. Organophosphate inhibition showed equivalent reactivity, indicating that the point mutation altered only the binding properties of the variant. Thus, Km and Ki changes explain the succinyldicholine sensitivity of people carrying the fluoride-2 variant.
The fluoride variant of human butyrylcholinesterase owes its name to the observation that it is resistant to inhibition by 0.050 mM sodium fluoride in the in vitro assay. Individuals who are heterozygous for the fluoride and atypical alleles experience about 30 min of apnea, rather than the usual 3-5 min, after receiving succinyldicholine. Earlier we reported that the atypical variant has a nucleotide substitution which changes Asp 70 to Gly. In the present work we have identified two different point mutations associated with the fluoride-resistant phenotype. Fluoride-1 has a nucleotide substitution which changes Thr 243 to Met (ACG to ATG). Fluoride-2 has a substitution which changes Gly 390 to Val (GGT to GTT). These results were obtained by DNA sequence analysis of the butyrylcholinesterase gene after amplification by PCR. The subjects for these analyses were 4 patients and 21 family members.
