F. Gounari et al., BOVINE FILENSIN POSSESSES PRIMARY AND SECONDARY STRUCTURE SIMILARITY TO INTERMEDIATE FILAMENT PROTEINS, The Journal of cell biology, 121(4), 1993, pp. 847-853
The cDNA coding for calf filensin, a membrane-associated protein of th
e lens fiber cells, has been cloned and sequenced. The predicted 755-a
mino acid-long open reading frame shows primary and secondary structur
e similarity to intermediate filament (IF) proteins. Filensin can be d
ivided into an NH2-terminal domain (head) of 38 amino acids, a middle
domain (rod) of 279 amino acids, and a COOH-terminal domain (tail) of
438 amino acids. The head domain contains a di-arginine/aromatic amino
acid motif which is also found in the head domains of various interme
diate filament proteins and includes a potential protein kinase A phos
phorylation site. By multiple alignment to all known IF protein sequen
ces, the filensin rod, which is the shortest among IF proteins, can be
subdivided into three subdomains (coils 1a, 1b, and 2). A 29 amino ac
id truncation in the coil 2 region accounts for the smaller size of th
is domain. The filensin tail contains 6 1/2 tandem repeats which match
analogous motifs of mammalian neurofilament M and H proteins. We sugg
est that filensin is a novel EF protein which does not conform to any
of the previously described classes. Purified filensin fails to form r
egular filaments in vitro (Merdes, A., M. Brunkener, H. Horstmann, and
S. D. Georgatos. 1991. J. Cell Biol. 115:397410), probably due to the
missing segment in the coil 2 region. Participation of filensin in a
filamentous network in vivo may be facilitated by an assembly partner.