Cytoplasmic Domain of Zebrafish Myelin Protein Zero: Adhesive Role Depends on -Conformation

¹ Boston College
² Istituto di Ricerche Farmacologiche

^* To whom correspondence should be addressed. E-mail: kirschnd{at}bc.edu.

Submitted on May 14, 2007
Revised on June 6, 2007
Accepted on 17 July 2007

	Abstract

Solution spectroscopy studies on the cytoplasmic domain of human myelin P0 (hP0-cyt) suggest that H-bonding between -strands from apposed molecules is likely responsible for the tight cytoplasmic apposition in compact myelin. As a follow-up to these findings, in the current study we used circular dichroism and x-ray diffraction to analyze the same type of model membranes previously used for hP0-cyt to investigate the molecular mechanism underlying the zebrafish cytoplasmic apposition. This space is significantly narrower in teleosts compared with that in higher vertebrates, and can be accounted for in part by the much shorter cytoplasmic domain in zebrafish (zP0-cyt). CD measurements on zP0-cyt showed similar structural characteristics as those of hP0-cyt, i.e., the protein underwent a structural transitions at lipid/protein (L/P) molar ratios >50, and adopted a -conformation at lower L/P molar ratios. X-ray diffraction was carried out on lipid vesicle solutions with zP0-cyt before and after dehydration to study the effect of protein on membrane lipid packing. Solution diffraction revealed the typical electron density profile for a single membrane bilayer. Diffraction patterns of dried samples suggested a multilamellar structure with the -folded P0-cyt located at the inter-membrane space. Our findings support the idea that the adhesive role of P0 at the cytoplasmic apposition in compact myelin depends on the cytoplasmic domain of P0 being in the -conformation.

Key Words: circular dichroism, lipids, membrane models, protein-protein interactions, teleost, x-ray diffraction