The carboxyl-terminal ahnak domain induces actin bundling and stabilizes muscle contraction.
Ahnak, a 700 kDa protein, is expressed in a variety of cells and has been implicated in different cell-type-specific functions. In the human heart, we observed an endogenous carboxyl-terminal 72 kDa ahnak fragment that copurified with myofibrillar proteins. Immunocytochemistry combined with confocal microscopy localized this fragment to the intercalated discs and close to the Z-line of cardiomyocytes. No endogenous myofibrillar ahnak fragment was observed in the skeletal muscle. We elucidated the role of the recombinant carboxyl-terminal ahnak fragment (ahnak-C2) in actin filament organization and in the function of muscle fibers. Addition of ahnak-C2 to actin filaments induced filament bundling into paracrystalline-like structures as revealed by electron microscopy. Incubation of demembranated skeletal muscle fibers with ahnak-C2 attenuated the decline in isometric force development upon repeated contraction-relaxation cycles. Our results suggest that the carboxyl-terminal ahnak domain exerts a stabilizing effect on muscle contractility via its interaction with actin of thin filaments.
Max Delbrück Center for Molecular Medicine, 13092 Berlin, Germany. haase@mdc-berlin.de
Hannelore
H
Haase
Ines
I
Pagel
Yana
Y
Khalina
Udo
U
Zacharzowsky
Veronika
V
Person
Gudrun
G
Lutsch
Daria
D
Petzhold
Monika
M
Kott
Jutta
J
Schaper
Ingo
I
Morano
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D021621:Imaging, Three-Dimensional; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure; D009206:Myocardium / Q000737:chemistry* / Q000648:ultrastructure; D009363:Neoplasm Proteins / Q000737:chemistry / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology
C075176:AHNAK protein, human; D000199:Actins; C489573:Ahnak protein, rat; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D011993:Recombinant Fusion Proteins