pfam16507: HEAT_PSME4_mid (This model is not part of the current CDD release)
Proteasome activator complex subunit 4, mid HEAT repeats region
The human Proteasome activator complex subunit 4 (PSME4, also known as PA200) and the yeast homologue BLM10 show 32 HEAT repeat-like modules, each comprising two helices joined by a turn, with adjacent repeats connected by a linker. Whereas a standard HEAT repeat is composed of ~50 residues, these HEAT repeats are highly variable. The length of helices ranges from 8 to 35 residues, turns range from 2 to 87 residues, and linkers range from 1 to 88 residues, with the longest linker, between HR21 and HR22, containing additional secondary structures (two strands and three helices). This entry represents the middle ordered region of the three in these proteins. BLM10 is found to surround the proteasome entry pore in the 1.2 MDa complex of proteasome and BLM10 to form a largely closed dome that is expected to restrict access of potential substrates. Thus BLM10 and PSME4 are predominantly nuclear and stimulate the degradation of model peptides, although they do not appear to stimulate the degradation of proteins, recognise ubiquitin, or utilize ATP.
Jiyao W et al.(2023). "The conserved domain database in 2023.",