The presence of Lys27 instead of Asn27 in human phospholamban promotes sarcoplasmic reticulum Ca2+-ATPase superinhibition and cardiac remodeling.
BACKGROUND
Phospholamban (PLN) is an inhibitor of the Ca2+ affinity of sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2). The amino acid sequence of PLN is highly conserved, and although all species contain asparagine (Asn), human PLN is unique in containing lysine (Lys) at amino acid 27.


RESULTS
Human PLN was introduced in the null background. Expression of human PLN, at similar levels to mouse wild-type PLN, resulted in significant decreases in the affinity of SERCA2 for Ca2+, attributed to unique spatial conformation of this PLN form and increases in its monomeric active unit compared with mouse PLN. The increased inhibition by human PLN was associated with attenuated cardiac contractility in the intact-animal, organ, and cardiomyocyte levels and with depressed calcium kinetics. These inhibitory effects could not be fully reversed even on maximal isoproterenol stimulation. There were no alterations in the expression levels of SERCA2, calsequestrin, ryanodine receptor, and FKBP12, although the sodium/calcium exchanger and the L-type Ca2+ channel expression levels were upregulated. The depressed function resulted in increased heart/body weight ratios and phosphorylation levels of Akt, p38, and Erk1/2.


CONCLUSIONS
Human PLN may play a more inhibitory role than that of other species in Ca2+ cycling. Expression of human PLN in the mouse is compensated by alterations in Ca2+-handling proteins and cardiac remodeling in an effort to normalize cardiac contractility. Thus, the unique amino acid sequence of human PLN may be critical in maintaining a high cardiac reserve, which is of paramount importance in the regulation of human cardiac function.
Zhao
Wen
W
Department of Pharmacology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0575, USA.
Yuan
Qunying
Q
Qian
Jiang
J
Waggoner
Jason R
JR
Pathak
Anand
A
Chu
Guoxiang
G
Mitton
Bryan
B
Sun
Xiaoyin
X
Jin
Jay
J
Braz
Julian C
JC
Hahn
Harvey S
HS
Marreez
Yehia
Y
Syed
Faisal
F
Pollesello
Piero
P
Annila
Arto
A
Wang
Hong-Sheng
HS
Schultz
Jo El J
Jel J
Molkentin
Jeffery D
JD
Liggett
Stephen B
SB
Dorn
Gerald W
GW
Kranias
Evangelia G
EG
D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D006332:Cardiomegaly / Q000209:etiology*; D006801:Humans; D007700:Kinetics; D008239:Lysine; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013045:Species Specificity; D000099211:Phospholamban
D001120:Arginine; D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D008239:Lysine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban; C506946:ATP2A2 protein, human; C506947:Atp2a2 protein, mouse