title: Engineering a switch-on peptide to ricin A chain for increasing its specificity towards HIV-infected cells.
abstract: BACKGROUND
  Ricin is a type II ribosome-inactivating protein (RIP) that potently inactivates eukaryotic ribosomes by removing a specific adenine residue at the conserved α-sarcin/ricin loop of 28S ribosomal RNA (rRNA). Here, we try to increase the specificity of the enzymatically active ricin A chain (RTA) towards human immunodeficiency virus type 1 (HIV-1) by adding a loop with HIV protease recognition site to RTA.
  
  
  METHODS
  HIV-specific RTA variants were constructed by inserting a peptide with HIV-protease recognition site either internally or at the C-terminal region of wild type RTA. Cleavability of variants by viral protease was tested in vitro and in HIV-infected cells. The production of viral p24 antigen and syncytium in the presence of C-terminal variants was measured to examine the anti-HIV activities of the variants.
  
  
  RESULTS
  C-terminal RTA variants were specifically cleaved by HIV-1 protease both in vitro and in HIV-infected cells. Upon proteolysis, the processed variants showed enhanced antiviral effect with low cytotoxicity towards uninfected cells.
  
  
  CONCLUSIONS
  RTA variants with HIV protease recognition sequence engineered at the C-terminus were cleaved and the products mediated specific inhibitory effect towards HIV replication.
  
  
  CONCLUSIONS
  Current cocktail treatment of HIV infection fails to eradicate the virus from patients. Here we illustrate the feasibility of targeting an RIP towards HIV-infected cells by incorporation of HIV protease cleavage sequence. This approach may be generalized to other RIPs and is promising in drug design for combating HIV.
authors.affiliation: Biochemistry Programme and Centre for Protein Science and Crystallography, School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
authors.forename: Ka-Yee
authors.initials: KY
authors.lastname: Au
authors.affiliation: Key Laboratory of Animal Models and Human Disease Mechanisms, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China.
authors.forename: Rui-Rui
authors.initials: RR
authors.lastname: Wang
authors.affiliation: Biochemistry Programme and Centre for Protein Science and Crystallography, School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
authors.forename: Yuen-Ting
authors.initials: YT
authors.lastname: Wong
authors.affiliation: Biochemistry Programme and Centre for Protein Science and Crystallography, School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China.
authors.forename: Kam-Bo
authors.initials: KB
authors.lastname: Wong
authors.affiliation: Key Laboratory of Animal Models and Human Disease Mechanisms, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China. Electronic address: zhengyt@mail.kiz.ac.cn.
authors.forename: Yong-Tang
authors.initials: YT
authors.lastname: Zheng
authors.affiliation: Biochemistry Programme and Centre for Protein Science and Crystallography, School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China. Electronic address: pcshaw@cuhk.edu.hk.
authors.forename: Pang-Chui
authors.initials: PC
authors.lastname: Shaw
mesh_terms: D000595:Amino Acid Sequence; D019380:Anti-HIV Agents / Q000494:pharmacology*; D001483:Base Sequence; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D015202:Protein Engineering; D017434:Protein Structure, Tertiary; D012276:Ricin / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D019380:Anti-HIV Agents; D012276:Ricin
keywords: HIV; Protease; Ribosome-inactivating protein; Ricin