Abstract

Haloarchaea, extremophilic microorganisms, possess unique membrane structures adapted to high-salinity environments. This study presents a comparative analysis of the structural organization of two distinct membrane types from a haloarchaeal species: the **purple membrane (PM)**, primarily composed of the light-driven proton pump bacteriorhodopsin, and the **claret membrane (CM)**, which represents the bulk cytoplasmic membrane. The primary objective was to elucidate the differences in lipid packing and protein arrangement between these specialized domains. We employed **Wide-Angle X-Ray Scattering (WAXS)** to probe the short-range order of the membrane components, specifically focusing on the lateral organization of the lipid acyl chains and the inter-helical spacing of membrane proteins. Our WAXS data reveal a significantly more ordered and rigid lipid matrix in the PM compared to the CM, suggesting that the high concentration and crystalline-like arrangement of bacteriorhodopsin impose substantial constraints on the surrounding lipids. Conversely, the CM exhibits a more fluid, liquid-crystalline phase, consistent with its role in general cellular transport and signaling. These findings provide critical insights into how extremophiles compartmentalize their cellular functions through differential membrane biophysics, highlighting the structural basis for the functional specialization of haloarchaeal membrane domains.