Small heat shock protein which functions as a molecular chaperone probably maintaining denatured proteins in a folding-competent state. Plays a role in stress resistance and actin organization. Homooligomer. Homodimer; becomes monomeric upon activation. Heterooligomer. Smooth, cardiac and skeletal muscle, hardly detectable in fibroblasts or focal contacts. Belongs to the small heat shock protein (HSP20) family.