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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

A Relaxed Specificity in Interchain Disulfide Bond Formation Characterizes the Assembly of a Low-Molecular-Weight Glutenin Subunit in the Endoplasmic Reticulum^1,[W],[OA]

Consiglio Nazionale delle Ricerche, Istituto di Biologia e Biotecnologia Agraria, I–20133 Milano, Italy (A.L., A.B., P.D.C., D.R., C.L.C., A.C.); Mathematics Institute, University of Warwick, Coventry CV4 7AL, United Kingdom (L.S.); and Dipartimento di Agrobiologia e Agrochimica, Università degli Studi della Tuscia, I–01100 Viterbo, Italy (S.M.)

Wheat (Triticum spp.) grains contain large protein polymers constituted by two main classes of polypeptides: the high-molecular-weight glutenin subunits and the low-molecular-weight glutenin subunits (LMW-GS). These polymers are among the largest protein molecules known in nature and are the main determinants of the superior technological properties of wheat flours. However, little is known about the mechanisms controlling the assembly of the different subunits and the way they are arranged in the final polymer. Here, we have addressed these issues by analyzing the formation of interchain disulfide bonds between identical and different LMW-GS and by studying the assembly of mutants lacking individual intrachain disulfides. Our results indicate that individual cysteine residues that remain available for disulfide bond formation in the folded monomer can form interchain disulfide bonds with a variety of different cysteine residues present in a companion subunit. These results imply that the coordinated expression of many different LMW-GS in wheat endosperm cells can potentially lead to the formation of a large set of distinct polymeric structures, in which subunits can be arranged in different configurations. In addition, we show that not all intrachain disulfide bonds are necessary for the generation of an assembly-competent structure and that the retention of a LMW-GS in the early secretory pathway is not dependent on polymer formation.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Aldo Ceriotti (ceriotti{at}ibba.cnr.it).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.127761

^* Corresponding author; e-mail ceriotti{at}ibba.cnr.it.

Received August 9, 2008; accepted November 6, 2008; published November 12, 2008.