High-speed atomic force microscopy: cooperative adhesion and dynamic equilibrium of junctional microdomain membrane proteins.
Junctional microdomains, paradigm for membrane protein segregation in functional assemblies, in eye lens fiber cell membranes are constituted of lens-specific aquaporin-0 tetramers (AQP0(4)) and connexin (Cx) hexamers, termed connexons. Both proteins have double function to assure nutrition and mediate adhesion of lens cells. Here we use high-speed atomic force microscopy to examine microdomain protein dynamics at the single-molecule level. We found that the adhesion function of head-to-head associated AQP0(4) and Cx is cooperative. This finding provides first experimental evidence for the mechanistic importance for junctional microdomain formation. From the observation of lateral association-dissociation events of AQP0(4), we determine that the enthalpic energy gain of a single AQP0(4)-AQP0(4) interaction in the membrane plane is -2.7 k(B)T, sufficient to drive formation of microdomains. Connexon association is stronger as dynamics are rarely observed, explaining their rim localization in junctional microdomains.
U1006 INSERM, Aix-Marseille Université, Parc Scientifique de Luminy, Marseille F-13009, France.
Adai
A
Colom
Ignacio
I
Casuso
Thomas
T
Boudier
Simon
S
Scheuring
D000818:Animals; D020346:Aquaporins / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D017630:Connexins / Q000737:chemistry* / Q000378:metabolism; D005136:Eye Proteins / Q000737:chemistry*; D007908:Lens, Crystalline / Q000737:chemistry / Q000378:metabolism; D021962:Membrane Microdomains / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization; D012756:Sheep
D020346:Aquaporins; D017630:Connexins; D005136:Eye Proteins; D008565:Membrane Proteins; C030328:aquaporin 0