A novel method for purifying recombinant human host defense cathelicidin LL-37 by utilizing its inherent property of aggregation

Yifeng Li, Xia Li, He Li, Oksana Lockridge, Guangshun Wang

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

The importance of human LL-37 in host defense and innate immunity is well appreciated as reflected by an exponential increase of relevant literature in Pub-Med. Although several articles reported the expression and purification of this cathelicidin, some protocols suffered from low efficiency in enzyme cleavage of fusion proteins due to aggregation and poor separation of recombinant LL-37 from the carrier protein on reverse-phase HPLC. We present a new method for purifying LL-37 that avoids both problems. In this method, the fusion protein (a tetramer) purified by metal affinity chromatography was readily cleaved at a thrombin site 30-residue upstream of the LL-37 sequence. The released LL-37-containing fragment formed a large soluble aggregate (∼95 kDa) at pH ∼7, allowing a rapid and clean separation from the carrier thioredoxin (∼14 kDa) by size-exclusion chromatography. Recombinant LL-37 was released from the isolated aggregate by chemical cleavage in 50% formic acid at 50 °C for 32 h. Due to a dramatic difference in retention time, recombinant LL-37 was well resolved from the S-Tag-containing peptide by RP-HPLC. Compared to previous procedures, the new method involves fewer steps and is highly reproducible. It increases peptide yield by 53%. NMR data support the aggregation of LL-37 into a tetramer with increase of pH as well as the feasibility of structural studies of an isotope-labeled antimicrobial peptide in the lipid micelle of dioctanoyl phosphatidylglycerol (D8PG) for the first time.

Original languageEnglish (US)
Pages (from-to)157-165
Number of pages9
JournalProtein Expression and Purification
Volume54
Issue number1
DOIs
StatePublished - Jul 2007

Keywords

  • Antimicrobial peptides
  • Cathelicidins
  • Chemical cleavage
  • Enzyme cleavage
  • Escherichia coli
  • FPLC
  • HPLC
  • LL-37
  • NMR
  • Protein aggregation

ASJC Scopus subject areas

  • Biotechnology

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