Investigation of self-assembling proline- and glycine-rich recombinant proteins and peptides inspired by proteins from a symbiotic fungus using atomic force microscopy and circular dichroism spectroscopy

Rhiannon G. Creasey, Nicolas H. Voelcker, Carolyn J. Schultz

Research output: Contribution to journalArticleResearchpeer-review

10 Citations (Scopus)

Abstract

Fiber-forming proteins and peptides are being scrutinized as a promising source of building blocks for new nanomaterials. Arabinogalactan-like (AGL) proteins expressed at the symbiotic interface between plant roots and arbuscular mycorrhizal fungi have novel sequences, hypothesized to form polyproline II (PPII) helix structures. The functional nature of these proteins is unknown but they may form structures for the establishment and maintenance of fungal hyphae. Here we show that recombinant AGL1 (rAGL1) and recombinant AGL3 (rAGL3) are extended proteins based upon secondary structural characteristics determined by electronic circular dichroism (CD) spectroscopy and can self-assemble into fibers and microtubes as observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). CD spectroscopy results of synthetic peptides based on repeat regions in AGL1, AGL2 and AGL3 suggest that the synthetic peptides contain significant amounts of extended PPII helices and that these structures are influenced by ionic strength and, at least in one case, by concentration. Point mutations of a single residue of the repeat region of AGL3 resulted in altered secondary structures. Self-assembly of these repeats was observed by means of AFM and optical microscopy. Peptide (APADGK)6 forms structures with similar morphology to rAGL1 suggesting that these repeats are crucial for the morphology of rAGL1 fibers. These novel self-assembling sequences may find applications as precursors for bioinspired nanomaterials. 

Original languageEnglish
Pages (from-to)711-722
Number of pages12
JournalBBA Proteins and Proteomics
Volume1824
Issue number5
DOIs
Publication statusPublished - May 2012
Externally publishedYes

Keywords

  • Amphipathic peptide
  • Arabinogalactan-like protein
  • Atomic force microscopy
  • Circular dichroism spectroscopy
  • Mycorrhizal symbiosis
  • Self-assembly

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