2FXM: Structure Of The Human Beta-myosin S2 Fragment

Myosin II is the major component of the muscle thick filament. It consists of two N-terminal S1 subfragments ("heads") connected to a long dimeric coiled-coil rod. The rod is in itself twofold symmetric, but in the filament, the two heads point away from the filament surface and are therefore not equivalent. This breaking of symmetry requires the initial section of the rod, subfragment 2 (S2), to be relatively flexible. S2 is an important functional element, involved in various mechanisms by which the activity of smooth and striated muscle is regulated. We have determined crystal structures of the 126 N-terminal residues of S2 from human cardiac beta-myosin II (S2-Delta), of both WT and the disease-associated E924K mutant. S2-Delta is a straight parallel dimeric coiled coil, but the N terminus of one chain is disordered in WT-S2-Delta due to crystal contacts, indicative of unstable local structure. Bulky noncanonical side chains pack into a/d positions of S2-Delta's N terminus, leading to defined local asymmetry and axial stagger, which could induce nonequivalence of the S1 subfragments. Additionally, S2 possesses a conserved charge distribution with three prominent rings of negative potential within S2-Delta, the first of which may provide a binding interface for the "blocked head" of smooth muscle myosin in the OFF state. The observation that many disease-associated mutations affect the second negatively charged ring further suggests that charge interactions play an important role in regulation of cardiac muscle activity through myosin-binding protein C.
PDB ID: 2FXMDownload
MMDB ID: 42787
PDB Deposition Date: 2006/2/6
Updated in MMDB: 2006/12
Experimental Method:
x-ray diffraction
Resolution: 2.7  Å
Source Organism:
Similar Structures:
Biological Unit for 2FXM: dimeric; determined by author and by software (PISA)
Molecular Components in 2FXM
Label Count Molecule
Proteins (2 molecules)
Myosin Heavy Chain, Cardiac Muscle Beta Isoform(Gene symbol: MYH7)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB