title: Molecular basis of an adult form of beta-hexosaminidase B deficiency with motor neuron disease.
abstract: A patient (KL) with progressive motor neuron disease associated with partial Hex A (alpha beta) and no Hex B (beta beta) activity, synthesized beta-chains which only associated with alpha-chains. To identify the molecular basis of this inability of beta-chains to self associate, RNA from cultured fibroblasts was reverse transcribed, the cDNA encoding the beta-chain amplified by polymerase chain reaction, subcloned, and sequenced to reveal two types of single missense mutation. The first mutation, (Type I) 619A----G, was paternally inherited and converted a 207IIe----Val in a highly conserved region believed to be associated with catalytic activity and activator protein binding. Biochemical evidence for impaired activator protein binding was obtained by purifying Hex A from KL urine and demonstrating a greater than 50% reduction of in vitro GM2 hydrolysis compared to normal urinary Hex A. In other cDNA species (Type II), a maternally inherited 1367A----C mutation converted 456Tyr----Ser in another highly conserved region of the beta-chain and we propose that this mutation leads to the inability of the beta-chains to self associate and thus reach maturity. These same cDNA species contained a second 362A----G mutation which converted 121Lys----Arg, but is apparently a polymorphism since it also occurs in some normal subjects. We propose that the patient is a compound heterozygote in which a combination of no self-association of the mutant beta-chains and impaired activator protein binding to alpha-beta (mutant) (Hex A) required for GM2 hydrolysis result in total beta-Hex B deficiency and slow accumulation of GM2 ganglioside, primarily in motor neurons.
authors.affiliation: Joseph P. Kennedy, Jr. Mental Retardation Research Center, Department of Pediatrics, University of Chicago, IL 60637.
authors.forename: P
authors.initials: P
authors.lastname: Banerjee
authors.forename: L
authors.initials: L
authors.lastname: Siciliano
authors.forename: D
authors.initials: D
authors.lastname: Oliveri
authors.forename: N R
authors.initials: NR
authors.lastname: McCabe
authors.forename: M J
authors.initials: MJ
authors.lastname: Boyers
authors.forename: A L
authors.initials: AL
authors.lastname: Horwitz
authors.forename: S C
authors.initials: SC
authors.lastname: Li
authors.forename: G
authors.initials: G
authors.lastname: Dawson
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005260:Female; D005347:Fibroblasts / Q000201:enzymology; D054818:Hexosaminidase A; D054819:Hexosaminidase B; D006801:Humans; D007527:Isoenzymes / Q000172:deficiency / Q000235:genetics* / Q000302:isolation & purification; D008297:Male; D008969:Molecular Sequence Data; D009046:Motor Neurons; D009154:Mutation; D009468:Neuromuscular Diseases / Q000201:enzymology / Q000235:genetics*; D009838:Oligodeoxyribonucleotides; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics; D012867:Skin / Q000201:enzymology; D001619:beta-N-Acetylhexosaminidases / Q000172:deficiency / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D007527:Isoenzymes; D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D012313:RNA; D004247:DNA; D054818:Hexosaminidase A; D054819:Hexosaminidase B; D001619:beta-N-Acetylhexosaminidases