Solution structure of the SEA domain from the murine homologue of ovarian cancer antigen CA125 (MUC16).
Human CA125, encoded by the MUC16 gene, is an ovarian cancer antigen widely used for a serum assay. Its extracellular region consists of tandem repeats of SEA domains. In this study we determined the three-dimensional structure of the SEA domain from the murine MUC16 homologue using multidimensional NMR spectroscopy. The domain forms a unique alpha/beta sandwich fold composed of two alpha helices and four antiparallel beta strands and has a characteristic turn named the TY-turn between alpha1 and alpha2. The internal mobility of the main chain is low throughout the domain. The residues that form the hydrophobic core and the TY-turn are fully conserved in all SEA domain sequences, indicating that the fold is common in the family. Interestingly, no other residues are conserved throughout the family. Thus, the sequence alignment of the SEA domain family was refined on the basis of the three-dimensional structure, which allowed us to classify the SEA domains into several subfamilies. The residues on the surface differ between these subfamilies, suggesting that each subfamily has a different function. In the MUC16 SEA domains, the conserved surface residues, Asn-10, Thr-12, Arg-63, Asp-75, Asp-112, Ser-115, and Phe-117, are clustered on the beta sheet surface, which may be functionally important. The putative epitope (residues 58-77) for anti-MUC16 antibodies is located around the beta2 and beta3 strands. On the other hand the tissue tumor marker MUC1 has a SEA domain belonging to another subfamily, and its GSVVV motif for proteolytic cleavage is located in the short loop connecting beta2 and beta3.
Maeda
Takeshi
T
RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan.
Inoue
Makoto
M
Koshiba
Seizo
S
Yabuki
Takashi
T
Aoki
Masaaki
M
Nunokawa
Emi
E
Seki
Eiko
E
Matsuda
Takayoshi
T
Motoda
Yoko
Y
Kobayashi
Atsuo
A
Hiroyasu
Fumiko
F
Shirouzu
Mikako
M
Terada
Takaho
T
Hayami
Nobuhiro
N
Ishizuka
Yoshiko
Y
Shinya
Naoko
N
Tatsuguchi
Ayako
A
Yoshida
Mayumi
M
Hirota
Hiroshi
H
Matsuo
Yo
Y
Tani
Kazutoshi
K
Arakawa
Takahiro
T
Carninci
Piero
P
Kawai
Jun
J
Hayashizaki
Yoshihide
Y
Kigawa
Takanori
T
Yokoyama
Shigeyuki
S
D000595:Amino Acid Sequence; D000818:Animals; D018394:CA-125 Antigen / Q000737:chemistry*; D017124:Conserved Sequence; D004247:DNA / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
D018394:CA-125 Antigen; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; C451759:MUC16 protein, human; D008565:Membrane Proteins; C549756:NBR1 protein, human; C486326:Nbr1 protein, mouse; D011506:Proteins; D004247:DNA