A heterozygous mutation of beta-actin associated with neutrophil dysfunction and recurrent infection

A human disorder caused by mutation in nonmuscle actin has not been reporte d. We report here a variant of nonmuscle actin in a female patient with rec urrent infections, photosensitivity, and mental retardation. She also had a bnormalities in neutrophil chemotaxis, superoxide production, and membrane potential response. Two-dimensional PAGE analysis of proteins from neutroph ils and other cell types from this patient demonstrated a unique protein sp ot migrating at 42 kDa with pI shifted slightly to neutral relative to norm al beta- and gamma-actin. Digestion peptide mapping and Western blotting sh owed this spot to be an abnormal actin. A full-length cDNA library was cons tructed by using mRNA from patient's cells and cDNA encoding the mutant bet a-actin molecule was identified by an in vitro translation method. Sequenci ng of the clones demonstrated a G-1174 to A substitution, predicting a glut amic acid-364 to lysine substitution in beta-actin and eliminating a HinfI DNase restriction site found in normal beta-actin sequence. By HinfI digest ion and by sequencing, the mutation in one allele of patient's genomic DNA was confirmed. Though no defect in cell-free polymerization of actin was de tected, this defect lies in a domain important for binding to profilin and other actin-regulatory molecules. In fact, the mutant actin bound to profil in less efficiently than normal actin did. Heterozygous expression of mutan t beta-actin in neutrophils and other cells of this patient may act in a do minant-negative fashion to adversely affect cellular activities dependent o n the function of nonmuscle actin.