Deduced Amino Acid Sequence of an α-Gliadin Gene from Spelt Wheat (Spelta) Includes Sequences Active in Celiac Disease

Cereal Chem. 76(4):548–551 The complete amino acid sequence of an α-type gliadin from spelt wheat (spelta) has been deduced from the cloned DNA sequence and compared with α-type gliadin sequences from bread wheat. The comparison showed only minor differences in amino acid sequences between the α-type gliadin from bread wheat and the α-type gliadin from spelta. The two sequences had an identity of 98.5%. Larger differences can be found between different α-type gliadin amino acid sequences from common bread wheat. Because all the different classes of gliadins, α, β, γ, and ω, appear to be active in celiac disease, it is reasonably certain that the spelta gliadin is also toxic. We conclude that spelta is not a safe grain for people with celiac disease, contrary to the implications in labeling a bread made from spelta as “an alternative to wheat”. Our conclusions are in accord with spelta and bread wheat being classed taxonomically as subspecies of the same genus and species, Triticum aestivum L. We have been approached by the leaders of celiac patient organizations in the United States to clarify the situation with regard to spelt (spelta) grain and celiac disease because so many of their members have heard that it is a safe alternative to wheat. We have also had anecdotal reports from them that some celiac patients who have tried spelta have been adversely affected by it. Spelta is touted as a miracle food by some health food companies in their product brochures and on the product labels. It is sometimes implied that spelta is safe for celiac patients and also for those with wheat allergy. We are not aware of any rigorous scientific evaluation of such claims. Recently, several scientific studies have been conducted to clarify the issue in regard to the compositional and nutritional claims made for spelta (Abdel-Aal et al 1995, 1998; Ranhotra et al 1995, 1996a,b). Although small compositional differences were found for the small numbers of samples in these studies, these differences are probably not significantly greater than what would be found if widely differing varieties of ordinary bread wheat were grown at widely different locations and in different crop years, so that environmental (soil, fertilizer, weather) and genetic differences were varied over their full range. Ranhotra et al (1996b), using a commercial antibody test for gluten, found that all spelt varieties tested positively. Abdel-Aal et al (1998) concluded that spelt wheats were not superior to modern bread and durum wheats in chemical composition. Spelta is, in fact, wheat even though it is often referred to as if it were a separate species (e.g., as Triticum spelta L.). Genetically, it is simply one of several closely related, fully interfertile subspecies of the hexaploid wheat, T. aestivum L. Common bread wheat belongs to the same species. As a subspecies, spelta is then named T. aestivum ssp. spelta (L.) Thell. (MacKey 1966, van Slageren 1994), and common bread wheat is named T. aestivum ssp. aestivum (Morris and Sears 1967, van Slageren 1994). Like bread wheat, spelta carries the AABBDD genomes. [See also URL http://www.ksu/wgrc/ Germplasm/Taxonomy/taxvsl.html. Sponsored by Kansas State University, Manhattan, KS.] The complex loci coding for gliadin proteins are closely homologous to those of bread wheat (Lafiandra et al 1989), and the proteins of spelt wheat varieties are similar to those of bread wheat cultivars in their gel electrophoretic patterns at acid pH, although some minor differences have been noted (Federmann et al 1992, Harsch et al 1997). Celiac disease is a condition in which susceptible individuals suffer enteropathy upon eating storage proteins from wheat, rye, and barley (Mäki and Collin 1997). Until recent years, oats have generally been considered harmful, but several recent, high-quality studies have found no harm from oats to patients with celiac disease or with dermatitis herpetiformis, a closely related skin condition (Janatuinen et al 1995, Srinvasan et al 1996, Hardman et al 1997, Reunala et al 1998). The current knowledge of toxic sequences in various grain proteins has been reviewed by Kasarda (1997). At the more extreme end of the spectrum of response to wheat, rye, and barley storage proteins in celiac disease, the intestinal mucosa of susceptible individuals is damaged by eating these grains and acquires a flattened appearance. The mucosal damage results in malabsorption of almost all nutrients, and symptoms can be diverse as a consequence (Howdle and Losowsky 1992, Mäki and Collin 1997). The fundamental mechanism by which the ingestion of wheat gluten proteins and their equivalents in rye and barley trigger a pathophysiological response that eventually may lead to intestinal damage is unknown, but an abnormal immune response to certain gliadin amino acid sequences has been the favored hypothesis in recent years (van de Wal et al 1998). Although there seems little basis for the claims that spelt is a satisfactory grain for celiac patients, these claims continue to be made (bread made from spelta has been found in health food stores labeled as an alternative to wheat). To provide further proof that spelta is not safe for celiac patients, we have cloned and sequenced the complete gene coding for a spelta α-type gliadin to compare the corresponding protein sequence with that of a wheat α-type gliadin (A-gliadin) (Kasarda et al 1984) that is almost certainly toxic in celiac disease. We also compare the spelta gliadin sequence with the sequences of small synthetic peptides that have been tested for toxicity in celiac disease. MATERIALS AND METHODS DNA Source, PCR Amplification, and Southern Blot Analyses DNA was extracted from the spelt wheat accession number ATRI 2021/SKL (var. arduini Mazz.) obtained from the Zentralinstitut für Genetik und Kulturpflanzenforschung, Gatersleben, Germany. Polymerase chain reaction (PCR) analyses were performed in a final reaction volume of 100 μL using 100-300 ng of genomic DNA, 2.5 units of Taq DNA polymerase (Boehringer, Germany), 1× Taq PCR buffer (Boehringer, Germany), 250 ng of each of the two primers, and 200 μM of each deoxyribonucleotide. Amplification conditions were for 30 cycles at 94°C for 1 min, 58°C for 2 min, and 72°C for 2 min. A final step at 72°C for 7 min was also performed. Oligonucleotides used as primers were synthesized on the basis of an α-gliadin sequence previously published (Anderson et al 1984, Reeves and Okita 1987) and have the following 1 U. S. Department of Agriculture, Agricultural Research Service, Western Regional Research Center, 800 Buchanan Street, Albany, CA 94710-1105. 2 Corresponding author. Phone: 510/559-5687. E-mail: [email protected] 3 Dipartimento di Agrobiologia e Agrochimica, Università degli Studi della Tuscia, Via S. Camillo de Lellis, 0100 Viterbo, Italy. Publication no. C-1999-0526-02R. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 1999.