L.G. Bobyleva, A.G. Bobylev, M.D. Shpagina, I.M. Vikhlyantsev, N.A. Freydina, Z.A. Podlubnaya

Amyloid deposits are the main symptom of amyloidoses, conformational diseases of humans and animals, occurring as a result of hereditary or acquired disorders of protein folding. Amyloid aggregates are observed in various neurodegenerative disorders, in particular Alzheimer's disease, Parkinson's, Huntington's fevers and prion diseases. Amyloid deposits were also found in the blood vessels, in cardiac and skeletal muscles, but the precursor proteins of these amyloid deposits have been little studied. Our previous studies have shown that proteins of titin family (titin, C-, X-, H-proteins) of skeletal and cardiac muscles are capable to form amyloid fibrils. In this work we tested the amyloid properties of smooth muscle protein smitin. Since smitin has a molecular structure similar to that for striated muscle titin, we suggested that smitin can also form amyloids. Using electron microscopy, we showed that smitin from rabbit stomach can form amorphous aggregates. Amyloid nature of the aggregates was confirmed by spectral methods, using specific dyes thioflavin T and Congo red. Thus, using the above methods, we identified the ability of the fifth muscle protein smitin to form amyloid aggregates, which denotes its ability to participate in the formation of amyloid deposits detected in organs and tissues in amyloidosis. Our next task is to find the conditions under which the smooth muscle protein smitin forms amyloid fibrils, and to estimate of their toxic properties.