期刊
FASEB JOURNAL
卷 21, 期 7, 页码 1383-1392出版社
FEDERATION AMER SOC EXP BIOL
DOI: 10.1096/fj.06-7644com
关键词
elastic filament titin; muscle atrophy; X-ray crystallography; binding studies
Titin forms an intrasarcomeric filament system in vertebrate striated muscle, which has elastic and signaling properties and is thereby central to mechanotransduction. Near its C-terminus and directly preceding a kinase domain, titin contains a conserved pattern of Ig and FnIII modules ( Ig(A168)- Ig(A169)-FnIII(A170), hereby A168-A170) that recruits the E3 ubiquitinligase MuRF-1 to the filament. This interaction is thought to regulate myofibril turnover and the trophic state of muscle. We have elucidated the crystal structure of A168-A170, characterized MuRF-1 variants by circular dichroism ( CD) and SEC-MALS, and studied the interaction of both components by isothermal calorimetry, SPOTS blots, and pull- down assays. This has led to the identification of the molecular determinants of the binding. A168-A170 shows an extended, rigid architecture, which is characterized by a shallow surface groove that spans its full length and a distinct loop protrusion in its middle point. In MuRF-1, a C- terminal helical domain is sufficient to bind A168-A170 with high affinity. This helical region predictably docks into the surface groove of A168-A170. Furthermore, pull- down assays demonstrate that the loop protrusion in A168-A170 is a key mediator of MuRF-1 recognition. Our findings indicate that this region of titin could serve as a target to attempt therapeutic inhibition of MuRF-1-mediated muscle turnover, where binding of small molecules to its distinctive structural features could block MuRF-1 access.
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