Pacifastin

Last updated
Pacifastin_I
PDB 1kio EBI.jpg
solution structure of the small serine protease inhibitor sgci[l30r, k31m]
Identifiers
SymbolPacifastin_I
Pfam PF05375
InterPro IPR008037
SCOP2 1kgm / SCOPe / SUPFAM

Pacifastin is a family of serine proteinase inhibitors found in arthropods. [1] [2] Pacifastin inhibits the serine peptidases trypsin and chymotrypsin. [3]

Contents

All pacifastin members that have been characterized at the molecular level are precursor peptides composed of an N-terminal signal sequence followed by a precursor domain and a variable number of inhibitor domains. Each of these inhibitor domains carries a six-cysteine motif – see below.

The first family members to be identified were isolated from Locusta migratoria migratoria (migratory locust) which were HI, LMCI-1 (PMP-D2) and LMCI-2 (PMP-C). [4] [5] [6] A further five members, SGPI-1 to 5, were then isolated from Schistocerca gregaria (desert locust), [7] [8] and a heterodimeric serine protease inhibitor was isolated from the haemolymph of Pacifastacus leniusculus (Signal crayfish), and named pacifastin. [9]

Function

Peptide proteinase inhibitors are in many cases synthesised as part of a larger precursor protein, referred to as a propeptide or zymogen, which remains inactive until the precursor domain is cleaved off in the lysosome, the precursor domain preventing access of the substrate to the active site until necessary. Proteinase inhibitors destined for secretion have an additional N-terminal signal-peptide domain which will be cleaved by a signal-peptidase. Removal of these one or two N-terminal inhibitor domains, either by interaction with a second peptidase or by autocatalytic cleavage, will activate the zymogen. [3]

Very little is known about the endogenous function of pacifastin-like inhibitors except that they may play roles in arthropod immunity and in regulation of the physiological processes involved in insect reproduction. [10]

Structure

The inhibitor unit of pacifastin is a conserved pattern of six cysteine residues (Cys1 – Xaa9–12 – Cys2 – Asn – Xaa – Cys3 – Xaa – Cys4 – Xaa2–3 – Gly – Xaa3–6 – Cys5 – Thr – Xaa3 – Cys6). Detailed analysis of the 3-D structure shows that these six residues form three disulfide bridges (Cys1–4, Cys2–6, Cys3–5), giving members of the pacifastin family a typical fold and remarkable stability. [11]

Pacifastin is a 155kDa protein composed of two covalently linked subunits, which are separately encoded. The heavy chain of pacifastin (105 kDa) is related to transferrins as it carries three transferrin lobes, two of which seem to be active in iron binding. [9] A number of the transferrin family members are also serine peptidases, and belong to MEROPS peptidase family S60 (INTERPRO). The light chain of pacifastin (44 kDa) is the proteinase inhibitory subunit, and consists of up to nine cysteine-rich inhibitory domains that are homologous to each other. The locust inhibitors share a conserved array of six residues with the pacifastin light chain. The structure of members of this family reveals that they consist of a triple-stranded antiparallel beta-sheet connected by three disulphide bridges. [9]

This family of serine protease inhibitors belongs to MEROPS inhibitor family I19, clan IW. They inhibit chymotrypsin, a peptidase belong to the S1 family (INTERPRO). [1]

Related Research Articles

In biology and biochemistry, protease inhibitors, or antiproteases, are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins.

Serine protease Class of enzymes

Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Serine proteases fall into two broad categories based on their structure: chymotrypsin-like (trypsin-like) or subtilisin-like.

Papain

Papain, also known as papaya proteinase I, is a cysteine protease enzyme present in papaya and mountain papaya.

Catalytic triad Set of three coordinated amino acids

A catalytic triad is a set of three coordinated amino acids that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes. An Acid-Base-Nucleophile triad is a common motif for generating a nucleophilic residue for covalent catalysis. The residues form a charge-relay network to polarise and activate the nucleophile, which attacks the substrate, forming a covalent intermediate which is then hydrolysed to release the product and regenerate free enzyme. The nucleophile is most commonly a serine or cysteine amino acid, but occasionally threonine or even selenocysteine. The 3D structure of the enzyme brings together the triad residues in a precise orientation, even though they may be far apart in the sequence.

Cysteine protease

Cysteine proteases, also known as thiol proteases, are enzymes that degrade proteins. These proteases share a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad or dyad.

Kallikreins are a subgroup of serine proteases, enzymes capable of cleaving peptide bonds in proteins. In humans, plasma kallikrein (KLKB1) has no known paralogue, while tissue kallikrein-related peptidases (KLKs) encode a family of fifteen closely related serine proteases. These genes are localised to chromosome 19q13, forming the largest contiguous cluster of proteases within the human genome. Kallikreins are responsible for the coordination of various physiological functions including blood pressure, semen liquefaction and skin desquamation.

Thermolysin

Thermolysin is a thermostable neutral metalloproteinase enzyme produced by the Gram-positive bacteria Bacillus thermoproteolyticus. It requires one zinc ion for enzyme activity and four calcium ions for structural stability. Thermolysin specifically catalyzes the hydrolysis of peptide bonds containing hydrophobic amino acids. However thermolysin is also widely used for peptide bond formation through the reverse reaction of hydrolysis. Thermolysin is the most stable member of a family of metalloproteinases produced by various Bacillus species. These enzymes are also termed 'neutral' proteinases or thermolysin -like proteinases (TLPs).

Adipokinetic hormone (AKH) is a short peptide hormone that has been studied in insects. It is a lipid mobilising hormone and is responsible for regulating fuel transport in the haemolymph, for redirecting energy to other processes as required by the insect.

Kexin is a prohormone-processing protease, specifically a yeast serine peptidase, found in the budding yeast. It catalyzes the cleavage of -Lys-Arg- and -Arg-Arg- bonds to process yeast alpha-factor pheromone and killer toxin precursors. The human homolog is PCSK4. It is a family of subtilisin-like peptidases. Even though there are a few prokaryote kexin-like peptidases, all kexins are eukaryotes. The enzyme is encoded by the yeast gene KEX2, and usually referred to in the scientific community as Kex2p. It shares structural similarities with the bacterial protease subtilisin. The first mammalian homologue of this protein to be identified was furin. In the mammal, kexin-like peptidases function in creating and regulating many differing proproteins.

Proteinase K

In molecular biology Proteinase K is a broad-spectrum serine protease. The enzyme was discovered in 1974 in extracts of the fungus Engyodontium album. Proteinase K is able to digest hair (keratin), hence, the name "Proteinase K". The predominant site of cleavage is the peptide bond adjacent to the carboxyl group of aliphatic and aromatic amino acids with blocked alpha amino groups. It is commonly used for its broad specificity. This enzyme belongs to Peptidase family S8 (subtilisin). The molecular weight of Proteinase K is 28,900 daltons.

KLK4

Kallikrein-related peptidase 4 is a protein which in humans is encoded by the KLK4 gene.

LEKTI

Lympho-epithelial Kazal-type-related inhibitor (LEKTI) also known as serine protease inhibitor Kazal-type 5 (SPINK5) is a protein that in humans is encoded by the SPINK5 gene.

SERPINB13

Serpin B13 is a protein that in humans is encoded by the SERPINB13 gene.

Crustacean cardioactive peptide (CCAP) is a highly conserved, amidated cyclic nonapeptide with the primary structure PFCNAFTGC-NH2 (ProPheCysAsnAlaPheTyrGlyCys-NH2) and a disulfide bridge between Cys3 and Cys9. It is found in crustaceans and insects where it behaves as a cardioaccelerator, neuropeptide transmitter for other areas of the nervous system and a hormone. CCAP was first isolated from the pericardial organs of the shore crab Carcinus maenas, where it has a role in regulating heartbeat. It was assumed that this was the peptide's main function and its name reflects this.

Corazonin is a highly conserved neuropeptide found in many insects, in particular locusts and cockroaches.

Bowman–Birk protease inhibitor

In molecular biology, the Bowman–Birk protease inhibitor family of proteins consists of eukaryotic proteinase inhibitors, belonging to MEROPS inhibitor family I12, clan IF. They mainly inhibit serine peptidases of the S1 family, but also inhibit S3 peptidases.

Kazal domain

The Kazal domain is an evolutionary conserved protein domain usually indicative of serine protease inhibitors. However, kazal-like domains are also seen in the extracellular part of agrins, which are not known to be protease inhibitors.

Hepacivirin is an enzyme. This enzyme catalyses the following chemical reaction:

Scytalidopepsin B

Scytalidocarboxyl peptidase B, also known as Scytalidoglutamic peptidase and Scytalidopepsin B is a proteolytic enzyme. It was previously thought to be an aspartic protease, but determination of its molecular structure showed it to belong a novel group of proteases, glutamic protease.

Sedolisin

The sedolisin family of peptidases are a family of serine proteases structurally related to the subtilisin (S8) family. Well-known members of this family include sedolisin ("pseudomonalisin") found in Pseudomonas bacteria, xanthomonalisin ("sedolisin-B"), physarolisin as well as animal tripeptidyl peptidase I. It is also known as sedolysin or serine-carboxyl peptidase. This group of enzymes contains a variation on the catalytic triad: unlike S8 which uses Ser-His-Asp, this group runs on Ser-Glu-Asp, with an additional acidic residue Asp in the oxyanion hole.

References

  1. 1 2 Rawlings ND, Tolle DP, Barrett AJ (2004). "Evolutionary families of peptidase inhibitors". Biochem J. 378 (Pt 3): 705–16. doi:10.1042/BJ20031825. PMC   1224039 . PMID   14705960.
  2. ↑ Breugelmans B, Simonet G, van Hoef V, Van Soest S, Vanden Broeck J (2009). "Pacifastin-related peptides: structural and functional characteristics of a family of serine peptidase inhibitors". Peptides. 30 (3): 622–32. doi:10.1016/j.peptides.2008.07.026. PMID   18775459. S2CID   8797134.
  3. 1 2 Parkinson NM, Conyers C, Keen J, MacNicoll A, Smith I, Audsley N, et al. (2004). "Towards a comprehensive view of the primary structure of venom proteins from the parasitoid wasp Pimpla hypochondriaca". Insect Biochem Mol Biol. 34 (6): 565–71. doi:10.1016/j.ibmb.2004.03.003. PMID   15147757.
  4. ↑ Boigegrain RA, Mattras H, Brehélin M, Paroutaud P, Coletti-Previero MA (December 1992). "Insect immunity: two proteinase inhibitors from hemolymph of Locusta migratoria". Biochem. Biophys. Res. Commun. 189 (2): 790–3. doi:10.1016/0006-291x(92)92271-x. PMID   1472051.
  5. ↑ Nakakura N, Hietter H, Van Dorsselaer A, Luu B (February 1992). "Isolation and structural determination of three peptides from the insect Locusta migratoria. Identification of a deoxyhexose-linked peptide". Eur. J. Biochem. 204 (1): 147–53. doi: 10.1111/j.1432-1033.1992.tb16617.x . PMID   1740125.
  6. ↑ Boigegrain RA, Pugnière M, Paroutaud P, Castro B, Brehélin M (February 2000). "Low molecular weight serine protease inhibitors from insects are proteins with highly conserved sequences". Insect Biochem. Mol. Biol. 30 (2): 145–52. doi:10.1016/s0965-1748(99)00109-5. PMID   10696590.
  7. ↑ Hamdaoui A, Wataleb S, Devreese B, Chiou SJ, Vanden Broeck J, Van Beeumen J, De Loof A, Schoofs L (January 1998). "Purification and characterization of a group of five novel peptide serine protease inhibitors from ovaries of the desert locust, Schistocerca gregaria". FEBS Lett. 422 (1): 74–8. doi: 10.1016/s0014-5793(97)01585-8 . PMID   9475173. S2CID   35980008.
  8. ↑ Gáspári Z, Patthy A, Gráf L, Perczel A (January 2002). "Comparative structure analysis of proteinase inhibitors from the desert locust, Schistocerca gregaria". Eur. J. Biochem. 269 (2): 527–37. doi: 10.1046/j.0014-2956.2001.02685.x . PMID   11856311.
  9. 1 2 3 Liang Z, Sottrup-Jensen L, Aspán A, Hall M, Söderhäll K (June 1997). "Pacifastin, a novel 155-kDa heterodimeric proteinase inhibitor containing a unique transferrin chain". Proc. Natl. Acad. Sci. U.S.A. 94 (13): 6682–7. Bibcode:1997PNAS...94.6682L. doi:10.1073/pnas.94.13.6682. PMC   21218 . PMID   9192625.
  10. ↑ Wang S, Cui Z, Liu Y, Li Q, Song C (2012). "The first homolog of pacifastin-related precursor in the swimming crab (Portunus trituberculatus): characterization and potential role in immune response to bacteria and fungi". Fish Shellfish Immunol. 32 (2): 331–8. doi:10.1016/j.fsi.2011.11.025. PMID   22154999.
  11. ↑ Breugelmans B, Simonet G, van Hoef V, Van Soest S, Smagghe G, Vanden Broeck J (2009). "A lepidopteran pacifastin member: cloning, gene structure, recombinant production, transcript profiling and in vitro activity". Insect Biochem Mol Biol. 39 (7): 430–9. doi:10.1016/j.ibmb.2009.03.005. PMID   19364530.
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