Myosin Binding Protein-C Forms Amyloid-Like Aggregates In Vitro

Abstract

This work investigated in vitro aggregation and amyloid properties of skeletal myosin binding protein-C (sMyBP-C) interacting in vivo with proteins of thick and thin filaments in the sarcomeric A-disc. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) found a rapid (5–10 min) formation of large (>2 μm) aggregates. sMyBP-C oligomers formed both at the initial 5–10 min and after 16 h of aggregation. Small angle X-ray scattering (SAXS) and DLS revealed sMyBP-C oligomers to consist of 7–10 monomers. TEM and atomic force microscopy (AFM) showed sMyBP-C to form amorphous aggregates (and, to a lesser degree, fibrillar structures) exhibiting no toxicity on cell culture. X-ray diffraction of sMyBP-C aggregates registered reflections attributed to a cross-β quaternary structure. Circular dichroism (CD) showed the formation of the amyloid-like structure to occur without changes in the sMyBP-C secondary structure. The obtained results indicating a high in vitro aggregability of sMyBP-C are, apparently, a consequence of structural features of the domain organization of proteins of this family. Formation of pathological amyloid or amyloid-like sMyBP-C aggregates in vivo is little probable due to amino-acid sequence low identity (<26%), alternating ordered/disordered regions in the protein molecule, and S–S bonds providing for general stability.

Nonspecific Amyloid Aggregation of Chicken Smooth-Muscle Titin: In Vitro Investigations

“…We revealed no such changes in the amyloid aggregation of chicken SMT HMW . Similar results have been obtained earlier for chicken SMT LMW [ 34 , 35 ] and for skeletal myosin binding protein C [ 46 ] that also consists of Ig-like and FnIII-like domains. It appears that the ability to form amyloid aggregates without changes in the secondary structure of molecules is a characteristic feature of the above-mentioned multidomain proteins, which distinguishes them from most other amyloid proteins.…”

“…The 10 Å reflex representing the distance between the beta sheets was blurred but was also present in both cases. According to numerous literature data, such reflexes are characteristic of amyloid or amyloid-like structures [ 46 ].…”