LMW glutenin

The sulfur-rich prolamins are quantitatively the most abundant group in wheat, barley and rye, accounting for approximately 80-90% of total prolamin fractions. They include polymeric and monomeric components and consist of at two families in each species, the B- and y-hordeins of barley two types of y-secalin of rye and a, 3 and y-gliadins and LMW glutenin subunits of wheat. The sulfur-poor prolamins include C-hordeins of barley, (O-secalin of rye and co-gliadin of wheat. 

Figure 13.11 SDS-PAGE of polymeric protein (after reduction to subunits). Group A HMW glutenin subunits showing x- and y-type subunits. Group B-, C-, D- LMW glutenin subunits. Arrow indicates subunit D [41].

P. Tosi, A. Giovangrossi, R. D Ovidio, F. Bekes, O. Larroque, J. Napier, and P. Shewry, Modification of the low molecular weight (LMW) glutenin composition of transgenic durum wheat effects on glutenin polymer size and gluten functionality. Mol. Breed. 16(2), 113-126 (2005). 

HMW MMW LMW Polymeric Monomeric Monomeric Polymeric HMW subunits of glutenins ai-Type gliadins a-Type and 7-type gliadins LMW subunits of glutenins HMW secalins ai-Secalins 40 K 7-secalins 75 K 7-secalins D-hordeins C-hordeins 7-Hordeins B-hordeins... 

Little is known about the precise organisation of the HMW and LMW subunits in glutenin polymers, but most researchers consider that the HMW subunits come from a disulphide-bonded network, with the LMW subunits acting as branches, possibly also providing some cross-links. The formation of such a network by the HMW subunits would be facilitated by the distribution of cysteine residues, which are predominantly located in the N-terminal (3 or 5 cysteines) and C-terminal (1 cysteine) domains (Figure 13.12). It would be possible for the HMW subunits to form polymers via head-to-tail disulphide bonds, with some cross-links (either directly or via LMW subunits) and branches. In addition, one or two intra-chain disulphide bonds could be formed within the N-terminal domains. The number and distribution of crosslinks within these glutenin polymers would undoubtedly contribute to their elastic properties. 

Low-molecular-weight glutenin subunit (LMW-GS) composition in common wheat is one of the critical determinants of gluten properties. However, the nomenclature of Glu-3 encoding LMW-GS has not been consistent among... 

Singh, N. K., K. W. Shepherd, and G. B. Cornish. 1991. A simplified SDS-PAGE procedure for separating LMW subunits of glutenin. Journal of Cereal Science 14 203-208. 

Figure 11.4 shows a schematic and simplified representation of the chromosomal locations of these genes. Glutenin subunits are coded by loci on group 1 chromosomes, the HMW-GS coded at the Glu-1 loci on the long arms, and the LMW-GS at the Glu-3 loci on the short arms. Two HMW-GS, denoted as x (lower mobility) and y (higher mobility) subunits, may be expressed at each of the three Glu-1 loci. In practice, both subunits are expressed at Glu-Dl, one or two at Glu-Bl, and one or zero at Glu-Al... 

Gupta, R. B., E MacRitchie, K. W. Shepherd, and R Ellison. 1991. Relative contributions of LMW and HMW glutenin subunits to dough strength and dough stickiness of bread wheat. In Gluten proteins 1990, ed. W. Bushuk and R. Tkachuk, 71-80. St. Paul, MN American Association of Cereal Chemists. 

---