Required for the correct formation of lens intermediate filaments as part of a complex composed of BFSP1, BFSP2 and CRYAA (By similarity). 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 (By similarity). Found in a complex composed of PPL (via C-terminal linker domain), BFSP1 and BFSP2 in the retinal lens (By similarity). Within the complex interacts with BFSP2 (By similarity). Interacts (via C-terminus) with MIP (via C-terminus) in aged lens fiber cells (PubMed:28259670). Abundantly expressed in both the inner and outer cortex of the retina, expressed at a lower level in the nucleus of the retina (at protein level) (PubMed:19875662). Detected in eye lens fiber cells (at protein level) (PubMed:7504675, PubMed:7588880). Proteolytically cleaved during lens cell fiber differentiation with increased fragmentation as fiber cell age increases. Myristoylated at Gly-433 following proteolytic cleavage at Asp-432. Acetylated at Ala-41 following proteolytic cleavage at Leu-40. Belongs to the intermediate filament family.