Modulation of fluorophore environment in host membranes of varying charge

Abstract

The net electrical charge of the biological membrane represents an important parameter in the organization, dynamics and function of the membrane. In this paper, we have characterized the change in the microenvironment experienced by a membrane-bound fluorescent probe when the charge of the phospholipids constituting the host membrane is changed from zwitterionic to cationic with minimal change in the chemical structure of the host lipid. In particular, we have explored the difference in the microenvironment experienced by the fluorescent probe 2-(9-anthroyloxy)stearic acid (2-AS) in model membranes of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cationic 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine (EPOPC) which are otherwise chemically similar, using the wavelength-selective fluorescence approach and other fluorescence parameters. Our results show that the microenvironment experienced by a membrane probe such as 2-AS is different in POPC and EPOPC membranes, as reported by red edge excitation shift (REES) and other fluorescence parameters. The difference in environment encountered by the probe in the two cases could possibly be due to variation in hydration in the two membranes owing to different charges.