Structural studies of a baboon (Papio sp.) plasma protein inhibitor of cholesteryl ester transferase

Abstract

A 38-residue protein associated with cholesteryl ester transfer inhibition has been identified in baboons~Papio sp.!. The cholesteryl ester transfer inhibitor protein~CETIP! corresponds to the N-terminus of baboon apoC-I. Relative to CETIP, baboon apoC-I is a weak inhibitor of baboon cholesteryl ester transferase~CET!. To study the structural features responsible for CET inhibition, CETIP was synthesized by solid-phase methods. Using sodium dodecyl sulfate~SDS! to model the lipoprotein environment, the solution structure of CETIP was probed by optical and 1 H NMR spectroscopy. Circular dichroism data show that the protein lacks a well-defined structure in water but, upon the addition of SDS, becomes helical~56%!. A small blue shift of 8 nm was observed in the intrinsic tryptophan fluorescence of CETIP in the presence of saturating amounts of SDS, suggesting that tryptophan-23 is not buried deeply in the lipid environment. The helical nature of CETIP in the presence of SDS was confirmed by upfield 1 H a secondary shifts and an average solution structure determined by distance geometry0simulated annealing calculations using 476 NOE-based distance restraints. The backbone~NϪC a ϪCϭO! root-mean-square deviation of an ensemble of 17 out of 25 calculated structures superimposed on the average structure was 1.06 6 0.30 Å using residues V4-P35 and 0.51 6 0.17 Å using residues A7-S32. Although the side-chain orientations fit the basic description of a class A amphipathic helix, both intramolecular salt bridge formation and "snorkeling" of basic side chains toward the polar face play minor, if any, roles in stabilizing the lipid-bound amphipathic structure. Conformational features of the calculated structures for CETIP are discussed relative to models of CETIP inhibition of cholesteryl ester transferase.

Determination of the Conformation of the Human VDAC1 N‐Terminal Peptide, a Protein Moiety Essential for the Functional Properties of the Pore

“…In aqueous environment at pH 5 the 1D 1 H NMR spectrum of the peptide exhibits narrow, well resolved resonances consistent with a monomeric polypeptide chain. [44,45] Some measured 3 J Ha,NH values were greater than 6.5 Hz, which is typical of conformational averaging. [43] Accordingly, the 2D NMR spectra collected under these conditions did not show any interresidue interactions that could indicate the preferred secondary structure of the polypeptide chain.…”

Snorkeling Preferences Foster an Amino Acid Composition Bias in Transmembrane Helices

“…39,40 On the other hand, Cushley and co-workers find little evidence for Lys snorkeling in another amphipathic helix. 41 Here, we analyze known membrane protein structures and demonstrate that polar side-chains in TM helices do indeed snorkel. We demonstrate that the ability of amino acids to snorkel in the appropriate direction is correlated with their N or C-terminal preferences.…”

The Wormlike Micellar Solution made of a Zwitterionic Surfactant (TDPS), an Anionic Surfactant (SDS), and Brine in the Semidilute Regime

“…Secondary structure predictions, nuclear magnetic resonance, and circular dichroism studies made on APO CI have revealed a high R-helix content, distributed in two R-helices. [14][15][16] The first R-helix (residues 4-30) presents approximately 7.5 periods (a period ) 3.6 amino acids of 5.4 Å pitch), while the second one (residues 35-53) consists of 5.2 periods. APO AII is a protein formed by two identical polypeptide chains bonded by a disulfide bridge at position 6, where each chain corresponds to 77 amino acid residues in length, and a molecular mass of 8.708 kDa.…”