1.C.85 The Pore-Forming Beta-Defensin (β-Defensin) Family

β-defensins are small antimicrobial polypeptides that are mainly expressed by epithelial cells and play an important role in the antimicrobial innate immune response. In addition to the direct microbicidal effects of these polypeptides, certain members of the β-defensin superfamily have the capacity to promote local innate inflammatory and systemic adaptive immune responses by interacting with the CC-chemokine receptor CCR6. Rohrl et al. (Rohrl et al. 2008) have identified mouse β-defensin 14 (mBD14, Defb14) as an orthologue of human β-defensin 3 (hBD3 or DEFB103). Based on primary structural analysis, mBD14 demonstrates greater (68%) homology to its human orthologue, containing three conserved cysteine linkages, characteristic of the β-defensin super family. mBD14 is expressed in a wide variety of tissues including spleen, colon, and tissues of the upper and lower respiratory tract. Rohrl et al. (Rohrl et al. 2008) also detected mBD14 expression in immature CD11c+ bone marrow-derived dendritic cells. The expression of mBD14 could be induced by Toll-like receptor agonists such as lipopolysaccharide and poly(I:C) and by pro-inflammatory stimuli e.g. tumor necrosis factor and interferon-gamma. Furthermore, expression of mBD14 seemed to be regulated by activation of the intracellular pattern recognition receptor NOD2/CARD15 as revealed by reporter gene analysis. Both hBD3 and mBD14 were chemotactic for freshly isolated mouse resident peritoneal cells. Thus, based on structural and functional similarities, mBD14 appears to be an orthologue of hBD3 (Rohrl et al., 2008).

β-defensins are important in mammalian immunity, displaying both antimicrobial and chemoattractant activities. These glycopeptides are mainly expressed in epithelial cells and have been shown to form pores in biological membranes (Zanich et al, 2003). Their 3-D structures are known (2NLS_A; Hover et al, 2000, Hover et al, 2001). Three canonical disulfide intramolecular bonds are believed to be dispensable for antimicrobial activity but essential for chemoattractant ability. However, HBD3 (human beta-defensin 3) alkylated with iodoactemide and devoid of any disulfide bonds is still a potent chemoattractant (Taylor et al., 2008). Furthermore, when the canonical six cysteine residues are replaced with alanine, the peptide is no longer active as a chemoattractant. The chemoattractant activities of HBD3 are restored by introduction of a single cysteine in the fifth position (Cys V) of the beta-defensin six cysteine motif. In contrast, a peptide with a single cysteine at the first position is inactive.

A range of overlapping linear fragments do not act as chemoattractants, suggesting that the chemotactic activity of this peptide is not dependent solely on an epitope surrounding Cys V. Full-length peptides either with alkylated cysteine residues or with cysteine residues replaced with alanine are still strongly antimicrobial. Defb14 peptide fragments were also tested for antimicrobial activity, and peptides derived from the N-terminal region display potent antimicrobial activity. Thus, the chemoattractant and antimicrobial activities of beta-defensins can be separated (Taylor et al., 2008), and both of these functions are independent of intramolecular disulfide bonds. These findings are important for further understanding of the mechanism of action of defensins and for therapeutic design.

The generalized transport reaction catalyzed by β-defensin is:

small molecules (in) small molecules (out)



This family belongs to the Defensin Superfamily.

 

References:

Colavita, I., E. Nigro, D. Sarnataro, O. Scudiero, V. Granata, A. Daniele, A. Zagari, A. Pessi, and F. Salvatore. (2015). Membrane protein 4F2/CD98 is a cell surface receptor involved in the internalization and trafficking of human β-Defensin 3 in epithelial cells. Chem Biol 22: 217-228.

Hoover, D.M., K.R. Rajashankar, R. Blumenthal, A. Puri, J.J. Oppenheim, O. Chertov, and J. Lubkowski (2000). The structure of human β- defensin-2 shows evidence of higher order oligomerization. J. Biol. Chem. 275: 32911-32988.

Hoover, D.M., O. Chertov, and J. Lubkowski. (2001). The structure of human β- defensin-1: new insights into structural properties of β- defensins. J. Biol. Chem. 276: 39021-39026.

Huang, C., J.R. Morlighem, H. Zhou, &.#.2.0.1.;.P. Lima, P.B. Gomes, J. Cai, I. Lou, C.D. Pérez, S.M. Lee, and G. Rádis-Baptista. (2016). The Transcriptome of the Zoanthid Protopalythoa variabilis (Cnidaria, Anthozoa) Predicts a Basal Repertoire of Toxin-like and Venom-Auxiliary Polypeptides. Genome Biol Evol 8: 3045-3064.

Röhrl, J., D. Yang, J.J. Oppenheim, and T. Hehlgans. (2008). Identification and biological characterization of mouse β- defensin 14, the orthologue of human β- defensin 3. J. Biol. Chem. 283: 5414-5419.

Sass, V., U. Pag, A. Tossi, G. Bierbaum, and H.G. Sahl. (2008). Mode of action of human β-defensin 3 against Staphylococcus aureus and transcriptional analysis of responses to defensin challenge. Int. J. Med. Microbiol. 298: 619-633.

Taylor, K., D.J. Clarke, B. McCullough, W. Chin, E. Seo, D. Yang, J. Oppenheim, D. Uhrin, J.R. Govan, D.J. Campopiano, D. MacMillan, P. Barran, and J.R. Dorin. (2008). Analysis and separation of residues important for the chemoattractant and antimicrobial activities of β- defensin 3. J. Biol. Chem. 283: 6631-6639.

Zanich, A., J.C. Pascall, and R. Jones. (2003). Secreted epididymal glycoprotein 2D6 that binds to the sperm's plasma membrane is a member of the β- defensin superfamily of pore-forming glycopeptides. Biol. Reprod. 69: 1831-1842.

Examples:

TC#NameOrganismal TypeExample
1.C.85.1.1β-defensin-1Animalsβ-defensin-1 of Homo sapiens (P60022)
 
1.C.85.1.2β-defensin-2Animalsβ-defensin 2 of Homo sapiens (O15263)
 
1.C.85.1.3β-defensin-3Animalsβ-defensin-3 of Homo sapiens (P81534)
 
1.C.85.1.4β-defensin-14Animalsβ-defensin-14 of Mus musculus (Q7TNV9)
 
1.C.85.1.5

Epididymus sperm-associated antigen (EP2E)

Mammals

EP2E of Homo sapiens (Q9H4P9)

 
1.C.85.1.6

β-defensin-2 of 71 aas and 1 TMS

Animals

Defensin β2 of Mus musculus

 
1.C.85.1.7

β-defensin 11 of 69 aas and 1 TMS

Animals

Defb11 of Rattus norvegicus

 
1.C.85.1.8

beta-Defensin 3 of 63 aas and 1 TMS (Colavita et al. 2015).  Sass et al. have proposed that interference with the organisation of membrane-bound multienzyme complexes such as the electron transport chain and the cell wall biosynthetic complex rather than on formation of defined transmembrane pores is responsible for death of Staphylococcus aureus (Sass et al. 2008).

BD3 pf Mus musculus

 
Examples:

TC#NameOrganismal TypeExample
1.C.85.2.1

Myotoxin-4 or Crotamine-4. Specifically modifies voltage-sensitive Na+ channels and exhibits analgesic effects. Belongs to the snake myotoxin family.

Snakes

Myotoxin-4 of Crotalus durissus terrificus (P24334)

 
1.C.85.2.2

Crotamine-IV-2 toxin of 42 aas and 0 TMSs

Animals

Croamine-IV-2 of Crotalus durissus cumanensis

 
1.C.85.2.3

β-defensin-like protein of 63 aas and 1 TMS

Animals

defensin-like protein of Bothrops matogrossensis (Pitviper) (Bothrops neuwiedi matogrossensis)

 
1.C.85.2.4

Crotamine-like precursor of 76 aas and 1 TMS.

Animals

Crotamine-like peptide of Thamnodynastes strigatus (Coastal house snake)

 
Examples:

TC#NameOrganismal TypeExample
1.C.85.3.1

Epithelial Gallinacin-1α. The full length antimicrobial peptide precursor is CHP2. Attacks bacteria and fungi. 

Birds

Gallinacin 1α of Gallus gallus (P46157)

 
1.C.85.3.2

β-defensin prepropeptide of 59 aas and 2 TMSs.

Animals

β-defensin of Meleagris gallopavo (turkey)

 
1.C.85.3.3
Avian beta-defensin, 5beta of 66 aas and 1 TMS.

Animals

Beta-defensin of Columba livia (domestic pigeon)
 
Examples:

TC#NameOrganismal TypeExample
1.C.85.4.1

Helofensin-1 lethal toxin of 183 aas (PMID 19837656).  This toxin possesses an inhibitory effect on electrical stimulation of the isolated hemi-diaphragm of mice. Neither hemorrhagic nor hemolytic activities were detected, but Huang et al. 2016 reported it to be a membrane active protein.

Helofensin-1 of Heloderma suspectum cinctum (Banded Gila monster)

 
1.C.85.4.2

Helofensin-3 (90% identical to helofensin-1) of 182 aas.  A lethal toxin.

Helofensin-3 of Heloderma suspectum cinctum (Banded Gila monster)

 
1.C.85.4.3

Uncharacterized protein of 172 aas

UP of Nematostella vectensis (Starlet sea anemone)