Isolation and characterization of cDNAs encoding the heavy chain of human inter-alpha-trypsin inhibitor (I alpha TI): unambiguous evidence for multipolypeptide chain structure of I alpha TI.
- 1 December 1987
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 84 (23) , 8272-8276
- https://doi.org/10.1073/pnas.84.23.8272
Abstract
Human inter-.alpha.-trypsin inhibitor (I.alpha.TI) is a plasma glycoprotein of Mr 180,000, which has been described as a single polypeptide chain. Recently, however, we proposed that I.alpha.TI might be composed of a heavy (H) chain (Mr = 95,000) and a light (L) chain (Mr = 40,000) synthesized by two separate mRNAs. In the present study we have characterized cDNAs for the H chain of I.alpha.TI. These cDNAs collectively covered two sequences (977 and 1450 base pairs in length) with single open reading frames. The deduced amino acid sequences were highly homologous to each other and well matched with partial amino acid sequences obtained from purified serum I.alpha.TI. RNA blot analyses of liver RNAs with H- or L-chain cDNAs as probes clearly identified two distinct mRNAs of 3.3 and 1.3 kilobases, which corresponded to H or L chain, respectively. Poly(A)+ RNAs hybrid-selected with H-chain cDNAs coded for polypeptide chains of Mr 90,000-95,000. These results unambiguously establish that I.alpha.TI is made of multipolypeptides, possibly including one H and two L chains. The H chain contains potential calcium-binding sites and also regions homologous to the proposed reactive site for thiol-proteinase inhibitors. These data indicate that I.alpha.TI is a complex, multifunctional protein. mRNAs for both the H and L chains were found only in liver.This publication has 20 references indexed in Scilit:
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