title: Transmembrane helix 11 is a genuine regulator of the endoplasmic reticulum Ca2+ pump and acts as a functional parallel of β-subunit on α-Na+,K+-ATPase.
abstract: The housekeeping sarco(endo)plasmic reticulum Ca(2+) ATPase SERCA2b transports Ca(2+) across the endoplasmic reticulum membrane maintaining a vital Ca(2+) gradient. Compared with the muscle-specific isoforms SERCA2a and SERCA1a, SERCA2b houses an 11th transmembrane segment (TM11) and a short luminal extension (LE) at its C terminus (2b-tail). The 2b-tail imposes a 2-fold higher apparent Ca(2+) affinity and lower V(max). Previously, we assumed that LE is the sole functional region of the 2b-tail and that TM11 is a passive element providing an additional membrane passage. However, here we show that peptides corresponding to the TM11 region specifically modulate the activity of the homologous SERCA1a in co-reconstituted proteoliposomes and mimic the 2b-tail effect (i.e. lower V(max) and higher Ca(2+) affinity). Using truncated 2b-tail variants we document that TM11 regulates SERCA1a independently from LE, confirming that TM11 is a second, previously unrecognized functional region of the 2b-tail. A phylogenetic analysis further indicates that TM11 is the oldest and most conserved feature of the 2b-tail, found in the SERCA pump of all Bilateria, whereas LE is only present in Nematoda and vertebrates. Considering remarkable similarities with the Na(+),K(+)-ATPase α-β interaction, we now propose a model for interaction of TM11 with TM7 and TM10 in the anchoring subdomain of the Ca(2+) pump. This model involves a TM11-induced helix bending of TM7. In conclusion, more than just a passive structural feature, TM11 acts as a genuine regulator of Ca(2+) transport through interaction with the pump.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Przemek A
authors.initials: PA
authors.lastname: Gorski
authors.forename: Catharine A
authors.initials: CA
authors.lastname: Trieber
authors.forename: Els
authors.initials: E
authors.lastname: Larivière
authors.forename: Marleen
authors.initials: M
authors.lastname: Schuermans
authors.forename: Frank
authors.initials: F
authors.lastname: Wuytack
authors.forename: Howard S
authors.initials: HS
authors.lastname: Young
authors.forename: Peter
authors.initials: P
authors.lastname: Vangheluwe
mesh_terms: D000818:Animals; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D009348:Nematoda / Q000201:enzymology / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506943:ATP2A1 protein, human; C506946:ATP2A2 protein, human; D000254:Sodium-Potassium-Exchanging ATPase