Molecular Characterization of a Zygote Wall Protein: An Extensin-Like Molecule in Chlamydomonas reinhardtii

Abstract

The green alga Chlamydomonas reinhardtii elaborates two biochemically and morphologically distinct cell walls during its life cycle: one surrounds the vegetative and gametic cell and the other encompasses the zygote. Hydroxyproline-rich glycoproteins (HRGPs) constitute a major component of both walls. We describe the isolation and characterization of a zygote-specific gene encoding a wall HRGP. The derived amino acid sequence of this alga1 HRGP is similar to those of higher plant extensins, rich in proline and serine residues and possessing repeating amino acid motifs, notably X(Pro), and (Ser-Pro),. Antiserum against this zygote wall protein detected common epitopes in several other zygote polypeptides, at least one of which is also encoded by a zygote-specific gene. We conclude that there is one set of HRGP wall genes expressed only in zygotes and another set that is specific to vegetative and gametic cells.

Domain conservation in several volvocalean cell wall proteins

“…1, lanes 1 and 5) using total RNA from 1-h-old C. reinhardtii zygotes, in which (SerPro)x-rich polypeptides have previously been described [56,57]. As expected, the 66 kDa Class VI protein [56] is the dominant signal observed in the immunoprecipitate.…”

“…In previous work, we demonstrated that a (SerPro)x motif is found in both zygote and vegetative cell wall proteins [53,56,57] suggesting that (SerPro)x repeats might be diagnostic for volvocalean cell wall proteins in the same manner that Ser(Pro)4 repeats are diagnostic of dicot extensins [57].…”

“…Incorporation varied from 15~o when using total RNA to 30-75~o with poly(A) + RNA. Immunoprecipitation with affinity-purified antiserum against a (SerPro)lo oligopeptide (e-(SerPro)10) and protein Asepharose CL.4B beads (Pharmacia) was performed as in Woessner and Goodenough [56]. For each immunoprecipitation assay, about 25 #Ci of incorporated label was used from the C. eugametos translation reactions and 4/~Ci was used from the C. reinhardtii translation reaction.…”

Sulfur Economy and Cell Wall Biosynthesis during Sulfur Limitation of Chlamydomonas reinhardtii

“…reinhardti contains a proteinaceous cell wall that is rich in sulfated, Hyp-containing glycoproteins or HRGPs (Miller et al, 1972(Miller et al, , 1974Roberts, 1974;Catt et al, 1976;Roberts et al, 1980;Adair and Apt, 1990;Ferris et al, 2001); these proteins often contain SerPro and/or X-(Pro) 3 repeat units, are frequently rich in Cys residues (Adair and Apt, 1990;Woessner and Goodenough, 1992;Woessner et al, 1994;Rodriguez et al, 1999;Suzuki et al, 2000), although not always (Woessner and Goodenough, 1989), and specific Figure 4. Accumulation of mRNA encoding Ecp76, Ecp88, arylsulfatase (Ars2), and ATP sulfurylase (Ats1).…”

“…Ecp88 contains no sulfur amino acids, whereas Ecp76 contains a single Met (and no Cys residues; Table II). Furthermore, both polypeptides are highly enriched for Leu, Ala, Gly, and Pro; a high proportion of these amino acids are present in several of the HRGPs (Adair and Appel, 1989;Woessner and Goodenough, 1989;Adair and Apt, 1990;Woessner et al, 1994).…”