Design, Synthesis, and Properties of Branch-Chained Maltoside Detergents for Stabilization and Crystallization of Integral Membrane Proteins: Human Connexin 26

A challenging requirement for structural studies of integral membrane proteins (IMPs) is the use of amphiphiles that replicate the hydrophobic envimment of membranes. Progress has been impeded by the limited number of useful detergents and the need for a deeper understanding of their structure activity relationships. To this end, we designed a family of detergents containing short, branched alkyl chains at the interface between the polar head and the apolar tail. This design mimics the second aliphatic chain of lipid molecules and reduces water penetration, thereby increasing the hydrophobicity within the interior of the micelle. To compare with the popular straight-chained maltoside detergents, the branch-chained beta-D-maltosides were synthesized efficiently in pure anomeric form. The branch-chained maltosides form smaller micelles by having shorter main chains, while having comparable hydrophobicity to the detergents with only straight chains. Selected branch-chained and straight-chained maltoside detergents were examined for their ability to solubilize, stabilize, and aid the crystallization of human connexin 26, an alpha-helical IMP that forms hexamers. We showed that the branch-chained maltosides with optimized micellar properties performed as well as or better than the straight-chained analogues and enabled crystallization in different space groups.