[Rotational mobility of membrane-bound Na,K-ATPase]

Area of Science:

• Biochemistry
• Membrane Protein Dynamics
• Enzyme Kinetics

Background:

• Na,K-ATPase (sodium-potassium adenosine triphosphatase) is crucial for ion transport in animal cells.
• Understanding its conformational changes and interactions is key to elucidating its function.
• Previous studies have indicated conformational flexibility, but detailed rotational mobility remains less understood.

Purpose of the Study:

• To investigate the rotational mobility of E1 and E2 conformers of duck salt gland Na,K-ATPase.
• To characterize the dynamics of the (alpha beta) protomer and potential protein associations.
• To explore the influence of temperature, pH, and experimental conditions on Na,K-ATPase rotational behavior.

Main Methods:

• Time-resolved phosphorescence anisotropy using eosine-5'-isothiocyanate (EITC) as a label.
• Analysis of rotational correlation times for different conformational states.
• Investigating the effects of temperature and pH on protein mobility and aggregation.

Main Results:

• Two distinct rotational mobility components were identified for both E1 and E2 conformers.
• A faster component (~15 microseconds) corresponds to the rotation of the (alpha beta) protomer (apparent radius 2.4 nm).
• A slower component (100-500 microseconds) suggests the formation of Na,K-ATPase associates or interactions with other membrane proteins.
• Increased temperature led to decreased fast component mobility and increased slow component mobility, indicating oligomerization.

Conclusions:

• Duck salt gland Na,K-ATPase exhibits complex rotational dynamics in the membrane.
• The enzyme exists as protomers and forms associates, with oligomerization influenced by temperature and pH.
• These findings provide insights into the structural organization and dynamic behavior of Na,K-ATPase within the cellular membrane.