Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled-coil arms

Freitag, Marvin; Jaklin, Sigrun; Padovani, Francesco; Radzichevici, Ecaterina; Zernia, Sarah; Schmoller, Kurt M. und Stigler, Johannes (2022): Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled-coil arms. In: Biophysical Journal, Bd. 121, Nr. 23: S. 4702-4713

Abstract

Structural maintenance of chromosome (SMC) complexes form ring-like structures through exceptional elon-gated coiled-coils (CCs). Recent studies found that variable CC conformations, including open and collapsed forms, which might result from discontinuities in the CC, facilitate the diverse functions of SMCs in DNA organization. However, a detailed descrip-tion of the SMC CC architecture is still missing. Here, we study the structural composition and mechanical properties of SMC proteins with optical tweezers unfolding experiments using the isolated Psm3 CC as a model system. We find a comparatively unstable protein with three unzipping intermediates, which we could directly assign to CC features by crosslinking experiments and state-of-the-art prediction software. Particularly, the CC elbow is shown to be a flexible, potentially non-structured feature, which divides the CC into sections, induces a pairing shift from one CC strand to the other and could facilitate large-scale confor-mational changes, most likely via thermal fluctuations of the flanking CC sections. A replacement of the elbow amino acids hin-ders folding of the consecutive CC region and frequently leads to non-native misalignments, revealing the elbow as a guide for proper folding. Additional in vivo manipulation of the elbow flexibility resulted in impaired cohesin complexes, which directly link the sensitive CC architecture to the biological function of cohesin. SIGNIFICANCE The detailed understanding of the molecular mechanisms of SMC complexes is important to identify the origin of chromosomal defects. The coiled-coil (CC) domains were recently found to undergo large-scale conformational changes, which enable diverse functions of these proteins. However, detailed structural information of the CCs is still elusive due to their high flexibility. By measuring mechanical responses, we identified thermodynamically relevant features in the CC that structure the CC in segments. One of these features, the elbow, additionally ensures proper alignment of flanking CC sections and can be viewed as a folding guide. Furthermore, in vivo manipulation of the elbow resulted in impaired complex function, showing the relevance of the CC features for SMC mechanics.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Chemie und Pharmazie > Department für Pharmazie - Zentrum für Pharmaforschung ; Chemie und Pharmazie > Department Biochemie
• Themengebiete: 500 Naturwissenschaften und Mathematik > 540 Chemie
• ISSN: 0006-3495
• Sprache: Englisch