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 (By similarity). Expressed in the deep and shallow cortices of the retina lens (at protein level). Proteolytically cleaved during lens cell fiber differentiation with increased fragmentation as fiber cell age increases. Myristoylated at Gly-427 following proteolytic cleavage at Asp-426. Acetylated at Ala-35 following proteolytic cleavage at Leu-34. Belongs to the intermediate filament family.