Primary structure of the (1→3,1→4)-β-D-glucan 4-glucohydrolase from barley aleurone

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Abstract
During germination of barley grains, the cell walls of the starchy endosperm are degraded by (1 .fwdarw. 3, 1 .fwdarw. 4)-.beta.-glucanases (EC 3.2.1.73) secreted from the aleurone and scutellar tissues. The complete sequence of the aleurone (1 .fwdarw. 3, 1 .fwdarw. 4)-.beta.-glucanase isoenzyme II comprises 306 amino acids and was determined by sequencing nine tryptic peptides (110 residues) and aligning them with the amino acid sequence deduced from a cDNA clone encoding the 291 NH2-terminal residues. Although no amino acid sequence homology with a bacterial (1 .fwdarw. 3) (1 .fwdarw. 4)-.beta. glucanase is apparent, close to 50% homology is found with two large regions of a (1 .fwdarw. 3)-.beta.-glucanase from tobacco pith tissue. The gene for barley (1 .fwdarw. 3, 1 .fwdarw. 4)-.beta.-glucanase isoenzyme II shares with that for the .alpha.-amylase isoenzyme 1 a strongly preferred use of codons with G and C in the wobble position (94% and 90%, respectively). Both enzymes are secreted from the aleurone cells during germination. Such one-sided codon usage is not characteristic for the gene encoding the (1 .fwdarw. 3)-.beta.-glucanase of tobacco pith tissue or the hor2-4 gene encoding the B1 hordein storage protein in the endosperm.