Small heat shock protein which functions as a molecular chaperone probably maintaining denatured proteins in a folding-competent state (By similarity). Seems to have versatile functions in various biological processes (By similarity). Plays a role in regulating muscle function such as smooth muscle vasorelaxation and cardiac myocyte contractility (By similarity). May regulate myocardial angiogenesis implicating KDR (By similarity). Overexpression mediates cardioprotection and angiogenesis after induced damage (PubMed:15105294). Stabilizes monomeric YWHAZ thereby supporting YWHAZ chaperone-like activity (By similarity). Homodimer (PubMed:19646995). Small heat shock proteins form high molecular mass oligomers containing variable number of monomers; these oligomers display a very flexible quaternary structure easily exchanging their subunits. Heterooligomer with HSPB1; formed through oligomerization of HSPB1:HSBP6 dimers; subunit exchange leads to formation of at least two different heterooligomeric complexes, differing in variable quantities of HSPB1 and HSPB6 homodimers in addition to HSPB1:HSPB6 heterodimers. Heterooligomer with CRYAB; large heterooligomers consist of CRYAB homodimers and HSPB5:HSPB6 heterodimers but lacking HSPB6 homodimers. Interacts with BAG3. Interacts (phosphorylated) with YWHAZ. Interacts with PDE4A and PDE4D; required for maintenance of the non-phosphorylated state of HSPB6 under basal conditions. Interacts with KDR. Interacts with PRKD1 (By similarity). Translocates to nuclear foci during heat shock. Widely expressed. High expression in muscle tissues. The N-terminus is blocked. Phosphorylated at Ser-16 by PKA and probably PKD1K; required to protect cardiomyocytes from apoptosis. Belongs to the small heat shock protein (HSP20) family.