Journal of Cereal Science 27 (1998) 15–22 Heterologous Expression and Dough Mixing Studies of Wild-Type and Mutant C Hordeins L. Tama ´ s*, F. Be ´ ke ´ s†, J. Greenfield‡, A.S . Tatham‡, P. W. Gras†, P. R. Shewry‡, and R. Appels§ *CSIRO, Division of Plant Industry, Canberra, ACT 2601, Australia †Plant Science CRC, CSIRO, Division of Plant Industry, North Ryde, NSW 2113, Australia ‡IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS18 9AF, U.K. §Plant Science CRC, GPO Box 475, Canberra, ACT 2601, Australia Received 7 August 1996 ABSTRACT Wild type and mutant (cysteine-containing) forms of C hordein were expressed in Escherichia coli. Incorporation of a mutant form with N- and C-terminal cysteine residues into dough using a 2g Mixograph showed similar positive effects on dough strength to the incorporation of HMW subunit 1Bx7. Co-incorporation showed that the effects of the two proteins were additive. In contrast, the incorporation of wild type C hordein or mutants with single cysteines at the N- or C-terminus resulted in decreased dough strength, with the two mutant forms inhibiting the positive effect of 1Bx7. Analysis of total protein extracts from the doughs indicate that the differences resulted from alterations in the proportions of gluten monomers, small gluten polymers and large gluten polymers.  1998 Academic Press Limited Keywords: wheat, Mixograph, C hordeins, HMW subunit, rheology, disulphide bonds. polymeric glutenins, and in particular of high M r INTRODUCTION polymers, is associated with good rheological and The rheological properties and, hence, the mixing breadmaking properties 2–4 . Such polymers are en- requirements of wheat flours and doughs are riched in high M r high molecular weight (HMW) largely determined by the amount and composition subunits of glutenin and genetic studies show clear of the gluten proteins, which are, in turn, in- correlations between the amount and composition fluenced by genetic and environmental factors. Of of this group of proteins and good or poor bread- particular interest is dough strength, measured making quality 5 . as mixing time in Mixograph studies, because A major limitation to evaluating the con- insufficient strength is often responsible for poor tributions of various groups of gluten proteins, and breadmaking quality 1 . Although the precise mo- of specific structural features of these proteins, to lecular basis for such properties is still poorly dough functionality has been the lack of ap- understood, it is clear that a high proportion of propriate test systems that allow specific proteins to be incorporated and tested within doughs. How- ever, due to two advances, the situation has re-  : HMW=high molecular weight; cently changed. The first is the development in PCR=polymerase chain reaction; HPLC=high per- our laboratory of a 2g Mixograph, together with formance liquid chromatography. procedures for incorporating exogenous proteins, Corresponding author: A. S. Tatham, e-mail:arthur.tatham@ bbsrc.ac.uk. including polymeric glutenins, into doughs 6–9 . This 0733–5210/98/010015+08 $25.00/0/jc970137  1998 Academic Press Limited