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Novel Cathelicidins from Pigeon Highlights Evolutionary Convergence in Avain Cathelicidins and Functions in Modulation of Innate Immunity.

Yu H, Lu Y, Qiao X, Wei L, Fu T, Cai S, Wang C, Liu X, Zhong S, Wang Y - Sci Rep (2015)

Bottom Line: In macrophages primed by LPS, Cl-CATH2 significantly down-regulated the gene and protein expressions of inducible nitric oxide synthase and pro-inflammatory cytokines while enhancing the anti-inflammatory cytokine, acting through MAPK and NF-κB signaling pathways.Molecular docking shows for the first time that cathelicidin binds to the opening region of LPS-binding pocket on myeloid differentiation factor 2 (MD-2) of toll-like receptor (TLR)4-MD-2 complex, which in turn inhibits the TLR4 pathway.Our results, therefore, provide new insight into the mechanism underlying the blockade of TLR4 signaling by cathelicidins.

View Article: PubMed Central - PubMed

Affiliation: School of Life Science and Biotechnology, Dalian University of Technology, Dalian, Liaoning 116024, China.

ABSTRACT
Cathelicidins are short cationic host defense peptides and play a central role in host innate immune system. Here we identified two novel cathelicidins, Cl-CATH2 and 3, from Columba livia. Evolutionary analysis of avian cathelicidins via phylogenetic tree and Ka/Ks calculations supported the positive selection that prompted evolution of CATH2 to CATH1 and 3, which originate from common ancestor and could belong to one superfamily. Cl-CATH2 and 3 both adopt amphipathic α-helical comformations identified by circular dichroism and the 3D structures built by Rosetta. Cl-CATH2 of CATH2 family with the most expression abundance in bird, exhibited relatively weak antimicrobial activity, but acted instead on the innate immune response without showing undesirable toxicities. In macrophages primed by LPS, Cl-CATH2 significantly down-regulated the gene and protein expressions of inducible nitric oxide synthase and pro-inflammatory cytokines while enhancing the anti-inflammatory cytokine, acting through MAPK and NF-κB signaling pathways. Molecular docking shows for the first time that cathelicidin binds to the opening region of LPS-binding pocket on myeloid differentiation factor 2 (MD-2) of toll-like receptor (TLR)4-MD-2 complex, which in turn inhibits the TLR4 pathway. Our results, therefore, provide new insight into the mechanism underlying the blockade of TLR4 signaling by cathelicidins.

No MeSH data available.


Related in: MedlinePlus

Overall structure of Cl-CATH2-TLR4-MD-2 Complex.(a–c) shows three views of Cl-CATH2 binding to mouse TLR4-MD-2 Complex. The N-terminal, central, and C-terminal domains of TLR4 are displayed in blue, cyan and green, respectively. The β-strands forming the MD-2 “cup” are colored in red and firebrick, and Cl-CATH2 is in magenta. (d) Energy versus rmsd plot. 1000 out of 10000 decoy structures from flexible docking study of TLR4-MD-2-Cl-CATH2 by RosettaDock. The horizontal axis represents the rmsd value compared to initial structure during flexible docking whereas the vertical axis represents the interface binding energy score of RosettaDock. (e) Closeup view of Cl-CATH2 binding to the mouse MD-2. Residues involved in interaction between Cl-CATH2 and MD-2 are displayed.
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f6: Overall structure of Cl-CATH2-TLR4-MD-2 Complex.(a–c) shows three views of Cl-CATH2 binding to mouse TLR4-MD-2 Complex. The N-terminal, central, and C-terminal domains of TLR4 are displayed in blue, cyan and green, respectively. The β-strands forming the MD-2 “cup” are colored in red and firebrick, and Cl-CATH2 is in magenta. (d) Energy versus rmsd plot. 1000 out of 10000 decoy structures from flexible docking study of TLR4-MD-2-Cl-CATH2 by RosettaDock. The horizontal axis represents the rmsd value compared to initial structure during flexible docking whereas the vertical axis represents the interface binding energy score of RosettaDock. (e) Closeup view of Cl-CATH2 binding to the mouse MD-2. Residues involved in interaction between Cl-CATH2 and MD-2 are displayed.

Mentions: Innate immunity is triggered by the binding of LPS, also known as one of the pathogen-associated molecular patterns, with pattern-recognition receptors, including TLRs33. Shortly after that, a broad, nonspecific innate immune response takes place, and the innate immune cells is triggered to secrete a range of inflammatory effectors3334. TLR4 was determined not to bind LPS alone, but form a TLR4-MD-2 complex with MD-2 protein that interacts with LPS3536. Whereafter LPS causes dimerization of the TLR4-MD-2 complex and initiates intracellular signaling37. To probe how Cl-CATH2 blocks the LPS-stimulated TLR4 signaling, the binding mode of Cl-CATH2 to TLR4-MD-2 complex was analyzed by molecular docking38. Cl-CATH2 binds to the C-terminal domains of MD-2 and cross over the MD-2 pocket edge, which covers the binding pockets of LPS, and in turn blocks the LPS binding to MD-2 followed by inhibition of TLR4 signaling (Fig. 6a–d). The mechanism for this Cl-CATH2-TLR4-MD-2 conformation possibly lies in lacking efficient hydrophobic interactions between Cl-CATH2 and interior of MD-2 pocket that is inclined to bind molecules like LPS with multiple hydrophobic acyl chains37. The interaction with Cl-CATH2 and MD-2 was principally mediated by ionic interactions, between Asp24 (Cl-CATH2)-Lys125 (MD-2) and tandem of Arg18-Phe19-Arg20 (Cl-CATH2) and Asp99-Asp100-Asp101 (MD-2) (Fig. 6e).


Novel Cathelicidins from Pigeon Highlights Evolutionary Convergence in Avain Cathelicidins and Functions in Modulation of Innate Immunity.

Yu H, Lu Y, Qiao X, Wei L, Fu T, Cai S, Wang C, Liu X, Zhong S, Wang Y - Sci Rep (2015)

Overall structure of Cl-CATH2-TLR4-MD-2 Complex.(a–c) shows three views of Cl-CATH2 binding to mouse TLR4-MD-2 Complex. The N-terminal, central, and C-terminal domains of TLR4 are displayed in blue, cyan and green, respectively. The β-strands forming the MD-2 “cup” are colored in red and firebrick, and Cl-CATH2 is in magenta. (d) Energy versus rmsd plot. 1000 out of 10000 decoy structures from flexible docking study of TLR4-MD-2-Cl-CATH2 by RosettaDock. The horizontal axis represents the rmsd value compared to initial structure during flexible docking whereas the vertical axis represents the interface binding energy score of RosettaDock. (e) Closeup view of Cl-CATH2 binding to the mouse MD-2. Residues involved in interaction between Cl-CATH2 and MD-2 are displayed.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f6: Overall structure of Cl-CATH2-TLR4-MD-2 Complex.(a–c) shows three views of Cl-CATH2 binding to mouse TLR4-MD-2 Complex. The N-terminal, central, and C-terminal domains of TLR4 are displayed in blue, cyan and green, respectively. The β-strands forming the MD-2 “cup” are colored in red and firebrick, and Cl-CATH2 is in magenta. (d) Energy versus rmsd plot. 1000 out of 10000 decoy structures from flexible docking study of TLR4-MD-2-Cl-CATH2 by RosettaDock. The horizontal axis represents the rmsd value compared to initial structure during flexible docking whereas the vertical axis represents the interface binding energy score of RosettaDock. (e) Closeup view of Cl-CATH2 binding to the mouse MD-2. Residues involved in interaction between Cl-CATH2 and MD-2 are displayed.
Mentions: Innate immunity is triggered by the binding of LPS, also known as one of the pathogen-associated molecular patterns, with pattern-recognition receptors, including TLRs33. Shortly after that, a broad, nonspecific innate immune response takes place, and the innate immune cells is triggered to secrete a range of inflammatory effectors3334. TLR4 was determined not to bind LPS alone, but form a TLR4-MD-2 complex with MD-2 protein that interacts with LPS3536. Whereafter LPS causes dimerization of the TLR4-MD-2 complex and initiates intracellular signaling37. To probe how Cl-CATH2 blocks the LPS-stimulated TLR4 signaling, the binding mode of Cl-CATH2 to TLR4-MD-2 complex was analyzed by molecular docking38. Cl-CATH2 binds to the C-terminal domains of MD-2 and cross over the MD-2 pocket edge, which covers the binding pockets of LPS, and in turn blocks the LPS binding to MD-2 followed by inhibition of TLR4 signaling (Fig. 6a–d). The mechanism for this Cl-CATH2-TLR4-MD-2 conformation possibly lies in lacking efficient hydrophobic interactions between Cl-CATH2 and interior of MD-2 pocket that is inclined to bind molecules like LPS with multiple hydrophobic acyl chains37. The interaction with Cl-CATH2 and MD-2 was principally mediated by ionic interactions, between Asp24 (Cl-CATH2)-Lys125 (MD-2) and tandem of Arg18-Phe19-Arg20 (Cl-CATH2) and Asp99-Asp100-Asp101 (MD-2) (Fig. 6e).

Bottom Line: In macrophages primed by LPS, Cl-CATH2 significantly down-regulated the gene and protein expressions of inducible nitric oxide synthase and pro-inflammatory cytokines while enhancing the anti-inflammatory cytokine, acting through MAPK and NF-κB signaling pathways.Molecular docking shows for the first time that cathelicidin binds to the opening region of LPS-binding pocket on myeloid differentiation factor 2 (MD-2) of toll-like receptor (TLR)4-MD-2 complex, which in turn inhibits the TLR4 pathway.Our results, therefore, provide new insight into the mechanism underlying the blockade of TLR4 signaling by cathelicidins.

View Article: PubMed Central - PubMed

Affiliation: School of Life Science and Biotechnology, Dalian University of Technology, Dalian, Liaoning 116024, China.

ABSTRACT
Cathelicidins are short cationic host defense peptides and play a central role in host innate immune system. Here we identified two novel cathelicidins, Cl-CATH2 and 3, from Columba livia. Evolutionary analysis of avian cathelicidins via phylogenetic tree and Ka/Ks calculations supported the positive selection that prompted evolution of CATH2 to CATH1 and 3, which originate from common ancestor and could belong to one superfamily. Cl-CATH2 and 3 both adopt amphipathic α-helical comformations identified by circular dichroism and the 3D structures built by Rosetta. Cl-CATH2 of CATH2 family with the most expression abundance in bird, exhibited relatively weak antimicrobial activity, but acted instead on the innate immune response without showing undesirable toxicities. In macrophages primed by LPS, Cl-CATH2 significantly down-regulated the gene and protein expressions of inducible nitric oxide synthase and pro-inflammatory cytokines while enhancing the anti-inflammatory cytokine, acting through MAPK and NF-κB signaling pathways. Molecular docking shows for the first time that cathelicidin binds to the opening region of LPS-binding pocket on myeloid differentiation factor 2 (MD-2) of toll-like receptor (TLR)4-MD-2 complex, which in turn inhibits the TLR4 pathway. Our results, therefore, provide new insight into the mechanism underlying the blockade of TLR4 signaling by cathelicidins.

No MeSH data available.


Related in: MedlinePlus