Filipin

Filipin is a polyene macrolide antibiotic produced by the actinomycete Streptomyces filipinensis. It comprises a family of related compounds, including filipin I, II, and III, which are primarily used today as fluorescent probes in membrane biology rather than as clinical antimicrobials.

Mechanism and properties: Filipin binds selectively to sterols, especially cholesterol, in membranes, forming insoluble 1:1 filipin-sterol complexes. Under ultraviolet excitation, the complex emits blue fluorescence, enabling visualization of cholesterol-rich domains in cell membranes by fluorescence microscopy. The staining is sensitive to the local sterol composition and can perturb membrane structure.

Applications and limitations: In research, filipin is used to map cholesterol distribution and to study membrane organization and lipid rafts. It is not used clinically and is not reliable for precise cholesterol quantification due to variable binding to different sterols and potential perturbation of membranes. Because filipin can be phototoxic and cytotoxic, staining is typically performed on fixed cells or membrane preparations, with minimal exposure to UV light.

Discovery and production: Filipin is produced by Streptomyces filipinensis and was originally identified in the context of antibiotic discovery. The name reflects its microbial producer and its antibiotic products; the compounds are now valued mainly for their utility as cholesterol stains in laboratory research.

Safety and handling: used only in controlled laboratory settings with appropriate safety protocols. See also: filipin staining, sterol-binding antibiotics.