title: Decreased interactions of mutant muscle LIM protein (MLP) with N-RAP and alpha-actinin and their implication for hypertrophic cardiomyopathy.
abstract: Previous work has shown that mutations in muscle LIM protein (MLP) can cause hypertrophic cardiomyopathy (HCM). In order to gain an insight into the molecular basis of the disease phenotype, we analysed the binding characteristics of wild-type MLP and of the (C58G) mutant MLP that causes hypertrophic cardiomyopathy. We show that MLP can form a ternary complex with two of its previously documented myofibrillar ligand proteins, N-RAP and alpha-actinin, which indicates the presence of distinct, non-overlapping binding sites. Our data also show that, in comparison to wild-type MLP, the capacity of the mutated MLP protein to bind both N-RAP and alpha-actinin is significantly decreased. In addition, this single point mutation prevents zinc coordination and proper folding of the second zinc-finger in the first LIM domain, which consequently renders the protein less stable and more susceptible to proteolysis. The molecular basis for HCM-causing mutations in the MLP gene might therefore be an alteration in the equilibrium of interactions of the ternary complex MLP-N-RAP-alpha-actinin. This assumption is supported by the previous observation that in the pathological situation accompanied by MLP down regulation, cardiomyocytes try to compensate for the decreased stability of MLP protein by increasing the expression of its ligand N-RAP, which might finally result in the development of myocyte disarray that is characteristic of this disease.
authors.affiliation: University of Potsdam, Department of Cell Biology, Institute of Biochemistry and Biology, Lennéstrasse 7a, Potsdam, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Gehmlich
authors.forename: Christian
authors.initials: C
authors.lastname: Geier
authors.forename: Karl Josef
authors.initials: KJ
authors.lastname: Osterziel
authors.forename: Peter F M
authors.initials: PF
authors.lastname: Van der Ven
authors.forename: Dieter O
authors.initials: DO
authors.lastname: Fürst
mesh_terms: D000185:Actinin / Q000378:metabolism*; D019943:Amino Acid Substitution / Q000235:genetics*; D001665:Binding Sites; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D060588:LIM Domain Proteins; D046912:Multiprotein Complexes / Q000378:metabolism; D032342:Muscle Cells / Q000378:metabolism / Q000473:pathology; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D017354:Point Mutation; D011485:Protein Binding; D020836:Protein Structure, Quaternary / Q000235:genetics / Q000502:physiology; D015032:Zinc / Q000378:metabolism
chemical_list: D060588:LIM Domain Proteins; D046912:Multiprotein Complexes; D009124:Muscle Proteins; C108533:NRAP protein, human; C090114:cysteine and glycine-rich protein 3; D000185:Actinin; D015032:Zinc