Calcium-modulated S100 protein-phospholipid interactions. An NMR study of calbindin D9k and DPC.
The cellular functions of several S100 proteins involve specific interactions with phospholipids and the cell membrane. The interactions between calbindin D(9k) (S100D) and the detergent dodecyl phosphocholine (DPC) were studied using NMR spectroscopy. In the absence of Ca(2+), the protein associates with DPC micelles. The micelle-associated state has intact helical secondary structures but no apparent tertiary fold. At neutral pH, Ca(2+)-loaded calbindin D(9k) does not associate with DPC micelles. However, a specific interaction is observed with individual DPC molecules at a site close to the linker between the two EF-hands. Binding to this site occurs only when Ca(2+) is bound to the protein. A reduction in pH in the absence of Ca(2+) increases the stability of the micelle-associated state. This along with the corresponding reduction in Ca(2+) affinity causes a transition to the micelle-associated state also in the presence of Ca(2+) when the pH is lowered. Site-specific analysis of the data indicates that calbindin D(9k) has a core of three tightly packed helices (A, B, and D), with a dynamic fourth helix (C) more loosely associated. Evidence is presented that the Ca(2+)-binding characteristics of the two EF-hands are distinctly different in a micelle environment. The role of calbindin D(9k) in the cell is discussed, along with the broader implications for the function of the S100 protein family.
Malmendal
Anders
A
Department of Biochemistry, Center for Structural Biology, 5140 BIOSCI/MRB III, Vanderbilt University, Nashville, Tennessee 37232-8725, USA. anders@chem.au.dk
Vander Kooi
Craig W
CW
Nielsen
Niels Chr
NC
Chazin
Walter J
WJ
D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D064026:Calbindins; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D003902:Detergents / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism*; D064030:S100 Calcium Binding Protein G / Q000737:chemistry* / Q000378:metabolism*; D009418:S100 Proteins / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
D001059:Apoproteins; D064026:Calbindins; D003902:Detergents; D008823:Micelles; D064030:S100 Calcium Binding Protein G; D009418:S100 Proteins; D010767:Phosphorylcholine; C028810:dodecylphosphocholine; D002118:Calcium