Required for the correct formation of lens intermediate filaments as part of a complex composed of BFSP1, BFSP2 and CRYAA (PubMed:27559293). Involved in altering the calcium regulation of MIP water permeability (By similarity). Part of a complex required for lens intermediate filament formation composed of BFSP1, BFSP2 and CRYAA (By similarity). Identified in a complex that contains VIM, EZR, AHNAK, BFSP1, BFSP2, ANK2, PLEC, PRX and spectrin (PubMed:21745462). Found in a complex composed of PPL (via C-terminal linker domain), BFSP1 and BFSP2 in the retinal lens (PubMed:19029034). Within the complex interacts with BFSP2 (PubMed:19029034). Interacts (via C-terminus) with MIP (via C-terminus) in aged lens fiber cells (By similarity). Detected in eye lens fiber cells (at protein level) (PubMed:14985306, PubMed:19029034, PubMed:21745462). Expressed in retinal lens epithelial cells (at protein level) (PubMed:27559293). First expressed in retinal lens fiber cells during elongation and differentiation, becoming localized to the cytoplasm as fiber cells mature and the beaded filament network forms at 3 weeks of age. Proteolytically cleaved during lens cell fiber differentiation with increased fragmentation as fiber cell age increases. Myristoylated at Gly-432 following proteolytic cleavage at Asp-431. Acetylated at Ala-35 following proteolytic cleavage at Leu-34. Complete loss of beaded filament structures in lens epithelial cells. Belongs to the intermediate filament family.