The structure of the central repetitive domain of high molecular weight (HMW) wheat gluten proteins was characterized in solution and in the dry state using HMW proteins Bx6 and Bx7 and a subcloned, bacterially expressed part of the repetitive domain of HMW Dx5. Model studies of the HMW consensus peptides PGQGQQ and GYYPTSPQQ formed the basis for the data analysis (van Dijk AA et al., 1997, Protein Sci 6:637-648). In solution, the repetitive domain contained a continuous nonoverlapping series of both type I and type I1 p-turns at positions predicted from the model studies; type I1 p-turns occurred at QPGQ and QQGY sequences and type I p-turns at YPTS and SPQQ. The subcloned part of the HMW Dx5 repetitive domain sometimes migrated as two bands on SDS-PAGE; we present evidence that this may be caused by a single amino acid insertion that disturbs the regular structure of p-turns. The type I p-turns are lost when the protein is dried on a solid surface, probably by conversion to type I1 p-turns. The homogeneous type I1 p-turn distribution is compatible with the formation of a P-spiral structure, which provides the protein with elastic properties. The p-turns and thus the P-spiral are stabilized by hydrogen bonds within and between turns. Reformation of this hydrogen bonding network after, e.g., mechanical disruption may be important for the elastic properties of gluten proteins.Keywords: elastic properties; repetitive proteins; structural characterization; wheat gluten proteins The central repetitive domain of high molecular weight proteins forms 60-80% of their amino acid sequence and is built from the consensus peptides PGQGQQ, GYYPTS(P/L)QQ, and GQQ Shewry et al., 1994). Its structural organization may consist of a series of p-turns that organize in a @spiral structure (Tatham et al., 1984;Shewry et al., 1994); this idea is supported by scanning tunneling microscopy images of HMW Dx5 (Miles et al., 1991). The proposed &spiral structure for HMW proteins is similar to that of elastin, where it forms the basis for the molecule's elastic properties (Uny, 1993). The structural analogy between HMW proteins and elastin suggests that the HMW proteins might have elastic properties as well; however, no Reprint requests to: G.T. Robillard, Department of Biochemistry and Biophysical Chemistry and the Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands; e-mail: G.T.Robillard@chem.rg.nl.'Present address: Gist Brocades N.V. Postbus 1, 2600 MA Delft, The Netherlands.Abbreviurions: FITR, fourier transform infrared; HMW, high molecular weight; IPTG, isopropyl-P-D-thiogalactopyranoside. detailed structural characterization of the HMW repetitive domain has been performed. In the companion paper (van Dijk et al., 1997), we described the structure of the consensus sequences of the repetitive domain using cyclic and linear peptides. We showed that they are highly structured and contain a mixture of type I and I1 p-turns that are stabilized by mu...

The high molecular weight (HMW) proteins from wheat contain a repetitive domain that forms 60‐80% of their sequence. The consensus peptides PGQGQQ and GYYPTSPQQ form more than 90% of the domain; both are predicted to adopt /3‐turn structure. This paper describes the structural characterization of these consensus peptides and forms the basis for the structural characterization of the repetitive HMW domain, described in the companion paper. The cyclic peptides cyclo‐[PGQGQQPGQGQQ] (peptide 1), cyclo‐[GYYPTSPQQGA] (peptide 2), and cyclo‐[PGQGQQGYYPTSPQQ] (peptide 3) were prepared using a novel synthesis route. In addition, the linear peptides (PGQGQQ) (n = 1, 3, 5) were prepared. CD, FTIR, and NMR data demonstrated a type II /3‐turn structure at QPGQ in the cyclic peptide 1 that was also observed in the linear peptides (PGQGQQ). A type I /3‐turn was observed at YPTS and SPQQ in peptides 2 and 3, with additional /3‐turns of either type I or II at GAGY (peptide 2) and QQGY (peptide 3). The proline in YPTS showed considerable cis/trans isomerization, with up to 50% of the population in the cis‐conformation; the other prolines were more than 90% in the trans conformation. The conversion from trans to cis destroys the type I /3‐turn at YPTS, but leads to an increase in turn character at SPQQ and GAGY (peptide 2) or QQGY (peptide 3).