Structure of the Threonine-Rich Extensin from Zea mays

Abstract

Chymotryptic digestion of a threonine-rich hydroxyproline-rich glycoprotein (THRGP) purified from the cell surface of a Zea mays cell suspension culture gave a peptide map dominated by the hexadecapeptide TC5: Thr-Hyp-Ser-Hyp-Lys-Pro-Hyp-Thr-ProLys-Pro-Thr-Hyp-Hyp-Thr-Tyr, in which the repetitive motif SerHyp-Lys-Pro-Hyp-Thr-Pro-Lys is homologous with the dominant decamer of P1-type dicot extensins: Ser-Hyp-Hyp-Hyp-Hyp-ThrHyp-Val-Tyr-Lys, modified by a Lys for Hyp substitution at residue 3, a Val-Tyr deletion at residues 8 and 9, and incomplete posttranslational modification of proline residues. One of the minor peptides (TC1) contained the 8-residue sequence: Thr-Hyp-SerHyp-Hyp-Hyp-Hyp-Tyr corresponding to the C-terminal tail (judging from the recently isolated maize cDNA clone MC56) which is homologous with the major repetitive motif of the 'P3' class of dicot extensins. Direct peptide sequencing defined potential glycosylated regions on the THRGP corresponding to clone MC56 and showing that glycosylated and nonglycosylated domains altemate with high regularity. The THRGP is not in the polyproline-11 conformation, judging from circular dichroic spectra, but nevertheless is an extended rod, from electron microscopic data. HFsolvolysis of cell walls from maize coleoptile, root, and root tip released deglycosylated THRGP detected on sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblots with high titer rabbit polyclonal antibodies raised against the intact THRGP. In a quantitative enzyme-linked immunosorbent assay, these antibodies cross-reacted 20% with tomato P1 extensin, and 18% with anhydrous hydrogen fluoride-deglycosylated P1. These results, together with other previously published data, show that maize THRGP is homologous with the dicot P1 extensins and, as such, is the first extensin isolated from a graminaceous monocot.In 1987, we reported (15) 2 Abbreviations: THRGP, threonine-hydroxyproline-rich glycoprotein; HRGP, hydroxyproline-rich glycoprotein; dTHRGP, deglycosylated threonine-hydroxyproline-rich glycoproteins; dw, dry weight; P1, glycosylated tomato extensin type 1; dPI, deglycosylated tomato extensin type P1; P2, glycosylated tomato extensin type 2; dP2, deglycosylated tomato extensin type 2; HHRGP, histidinehydroxyproline-rich glycoprotein; dHHRGP, deglycosylated histidine-hydroxyproline-rich glycoprotein; HF, anhydrous hydrogen fluoride; OPA, orthophthalaldehyde; HFBA, hepta-fluorobutyric acid; AGP, arabinogalactan protein; AP, alkaline phosphatase. CD, circular dichroism; ABTS, 2,2'-Azino-bis(3-ethylbenzthiazinoline-6-sulfonic acid).ceous monocot Zea mays and provided evidence that this HRGP may be an extensin, a class ofextended rodlike HRGPs well known as structural components of the dicot primary cell wall. Like a typical extensin, this protein is highly basic, rich in hydroxyproline and proline, 0-glycosylated through hydroxyproline residues with one to four arabinosyl residues, and was visualized by transmission EM as a flexuous rod. Furthermore, antibodies raised ...

Identification and Molecular Characterization of Novel Peroxidase with Structural Protein-like Properties

“…Moreover, the novel features are also found in the locations of proline residues in peroxidase 1. Peroxidase 1 possesses three proline-rich regions in its molecule, and these amino acid sequences are also found in those predicted from genes encoding tobacco extensin (28), maize extensin (29), and a giant cockroach structural protein (30), assuming that this isozyme can act as a structural protein. In contrast, peroxidases 2 and 3 have no significant characteristics except for regions with high homology to other plant peroxidases.…”

“…The sequences in the first and second proline-rich regions (Ser-ProPro and Pro-Pro-Pro-Ser, respectively) were also found in the amino acid sequence predicted from the nucleotide sequence of tobacco extensin gene (28). Maize extensin gene was shown to encode repeats of a proline-rich motif consisting of 16 amino acids (29), partial sequence of which was identical with that (Pro-Pro-Thr-Pro) in the third proline-rich region. Surprisingly, the amino acid sequence (Val-Val-Pro-Met-Asp-Pro-ProThr-Pro-Ala) of the third region were found to bear 80% identity and 90% homology to a region (Val-Val-Pro-Val-Asp-AlaPro-Thr-Pro-Ala) of the structural proteins of the giant cockroach (Blaberus craniifer) (30).…”

Role of the Extensin Superfamily in Primary Cell Wall Architecture

“…Again, a simple answer suggests that some evolutionary lines, notably grasses, have founded mechanical support systems largely involving non-HRGP structural proteins (Kieliszewski and Lamport, 1987;Kieliszewski et al, 1990) but perhaps retain the primary role of extensin as a self-assembling amphiphile with a templating role at cytokinesis.…”

Molecular basis of barley quality

“…However, very few have been identified as having an impact on quality. Cell walls contain glycine-rich protein, as well as threonine-rich and hydroxyproline-rich glycoproteins (Cassab and Varner 1988;Kieliszewski et al 1990). A structural protein, friabilin, has been isolated from barley endosperm.…”