A new extra sequence at the amino terminal of a μ heavy chain disease protein (DAG)

Abstract The primary structure of a human μ heavy chain (DAG) protein is described. The native protein is a circular decamer with a molecular weight ( M r) of 500 kDa, each decamer being constituted of the constant domainsC μ 2 , C μ 3 and C μ 4 and interlinked by 15 disulfide bridges. At its NH 2 -terminal each monomeric chain starts with an “extra sequence”. The amino acid sequence of this segment is Arg-Gln-Ser-Asp-Asp-Pro-Val-Leu-Arg-Gly-Thr-Thr-Val-Pro-Val-Thr-Glu and its reinitiation point is located at Val 223 (Gal numbering), at the beginning of Cμ 2 . This sequence has no homology with any other protein included in the present databases.