Properties of the C-terminal domain of 4.1 proteins.
At the C-terminus of all known 4.1 proteins is a sequence domain unique to these proteins, known as the C-terminal domain (CTD). Mammalian CTDs are associated with a growing number of protein-protein interactions, although such activities have yet to be associated with invertebrate CTDs. Mammalian CTDs are generally defined by sequence alignment as encoded by exons 18-21. Comparison of known vertebrate 4.1 proteins with invertebrate (Caenorhabditis elegans and Drosophila melanogaster) 4.1 proteins indicates that mammalian 4.1 exon 19 represents a vertebrate adaptation that extends the sequence of the CTD with a Ser/Thr-rich sequence. The CTD was first described as a 22/24-kDa domain by chymotryptic digestion of erythrocyte 4.1 (4.1R) [Leto, T.L. & Marchesi, V.T. (1984) J. Biol. Chem. 259, 4603-4608]. Here we show that in 4.1R the 22/24-kDa fragment is not stable but rapidly processed to a 15-kDa fragment by chymotrypsin. The 15-kDa fragment is extremely stable, being resistant to overnight digestion in chymotrypsin on ice. Analysis of this fragment indicates that it is derived from residues 709-858 (SwissProt accession no. P48193), and represents the CTD of 4.1R. The fragment behaves as a globular monomer in solution. Secondary-structure predictions indicate that this domain is composed of five or six beta strands with an alpha helix before the most C-terminal of these. Together these data indicate that the CTD probably represents an independent folding structure which has gained function since the divergence of vertebrates from invertebrates.
Scott
C
C
Department of Biosciences, University of Kent, Canterbury, Kent, UK.
Phillips
G W
GW
Baines
A J
AJ
D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016208:Databases, Factual; D004331:Drosophila melanogaster / Q000235:genetics; D004912:Erythrocytes / Q000737:chemistry; D005091:Exons; D006801:Humans; D007448:Invertebrates; D008322:Mammals; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009479:Neuropeptides; D010446:Peptide Fragments / Q000737:chemistry; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D012984:Software
D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D009479:Neuropeptides; D010446:Peptide Fragments; C028841:erythrocyte membrane band 4.1 protein; C120557:erythrocyte membrane protein band 4.1-like 1; D002918:Chymotrypsin