title: Functional Basis of Three New Recessive Mutations of Slow Skeletal Muscle Troponin T Found in Non-Amish TNNT1 Nemaline Myopathies.
abstract: Troponin T (TnT) is the tropomyosin (Tm)-binding and thin filament-anchoring subunit of troponin and plays a central role in striated muscle contraction. A nonsense mutation in exon 11 of the TNNT1 gene encoding slow skeletal muscle troponin T (ssTnT) truncating the polypeptide chain at Glu(180) causes a lethal recessive nemaline myopathy (NM) in the Amish (ANM). More TNNT1 NM mutations have been reported recently with similar recessive phenotypes. A nonsense mutation in exon 9 causes truncation at Ser(108), and a splicing site mutation causes truncation at Leu(203). Another splicing site mutation causes an internal deletion of the 39 exon 8-encoded amino acids. We engineered and characterized these ssTnT mutants to demonstrate that the Ser(108) truncation exhibits a Tm binding affinity lower than that of the ANM Glu(180) truncation, indicating a partial loss of Tm-binding site 1. Despite the presence of Tm-binding sites 1 and 2, ssTnT truncated at Leu(203) binds Tm with decreased affinity, consistent with its recessive NM phenotype and the requirement of troponin complex formation for high-affinity binding of TnT to Tm. The exon 8-deleted ssTnT has a partial loss of Tm-binding site 1 but retains high-affinity Tm-binding site 2. However, exon 8-deleted ssTnT exhibits a dramatically diminished Tm binding affinity, indicating a long-range conformational effect of this middle region deletion. Predicted from the TnT structure-function relationship, removal of the N-terminal variable region partially rescued this negative impact. These novel findings lay a foundation for understanding the pathogenesis of TNNT1 myopathies and provide insights into the development of targeted treatment.
authors.affiliation: Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States.
authors.forename: Chinthaka
authors.initials: C
authors.lastname: Amarasinghe
authors.affiliation: Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States.
authors.forename: M Moazzem
authors.initials: MM
authors.lastname: Hossain
authors.affiliation: Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States.
authors.forename: J-P
authors.initials: JP
authors.lastname: Jin
mesh_terms: D005091:Exons / Q000235:genetics; D006801:Humans; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000378:metabolism*; D009154:Mutation; D017696:Myopathies, Nemaline / Q000235:genetics / Q000378:metabolism*; D000072756:Protein Conformation, alpha-Helical; D015202:Protein Engineering; D013329:Structure-Activity Relationship; D020107:Troponin T / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D020107:Troponin T