Struktura proteina srži hepatitis B virusa i njegove interakcije s proteinima virusne ovojnice

undergraduate thesis

• Title (english): Structure of the hepatitis B virus core protein and its interactions with the envelope proteins
• Author: Iva Pritišanac
• Mentor: Mirna Ćurković-Perica (mentor)
• Granter: University of Zagreb; Faculty of Science; (Department of Biology); Zagreb
• Defense date and country: 2011, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Biology

Abstract

Virus hepatitisa B (HBV) je član Hepadna virusne obitelji s ovojnicom i neobičnim, djelomično dvostrukim DNA genomom. Prevladavajući oblik virusne srži, in vivo, je sferična proteinska čestica, 34 nm u promjeru, T = 4 ikosaedarne simetrije, građena od 240 monomera proteina srži HBV(HBc). Protein srži ima molekulsku težinu 22 kD te 183-185 duge sekvence aminokiselina koja se sastoji od dvije strukturno i funkcionalno različite regije. N-terminalnu regiju, nazvanu i domena slaganja, čine prvih 149-151 aminokiselina. Ova je regija posve samostalna u usmjeravanju funkcionalnog smatanja monomera proteina srži i posljedično sklapanje same srži. 34 aminokiseline duga C-terminalna domena, posve je neophodna za smatanje proteina i sklapanje srži te budući da je izuzetno bogata konzerviranim argininskim (R) amino kiselinama ima ulogu u slaganju kompleksa pre-genomske RNA/reverzna transkriptaze u sklapajuću proteinsku srž. Krio-elektronsko mikroskopske analize i proteinska X-ray kristalografija na srži HBV ukazala su na neočekivanu dominaciju α zavojnica u tercijarnoj strukturi monomera, s dugom α-helikalnom ukosnicom dviju zavojnica (α3 i α4) kao njezinom osnovom. Amfipatske α-helikalne ukosnice dvaju monomera, interakcijom tvore kompaktan dimer, čije sučelje pokriva veliku površinu hidrofobnih bočnih lanaca individualnih monomera. Hidrofobne interakcije, predstavljaju glavnu pokretaču snagu za spontano sklapanje dimera te ujedno čine osnovu stabilnosti čitave srži. Dvije α-helikalne ukosnice okupljaju u dimeru četiri α uzvojnice, koje tako čine četvero-helikalni snop, osobitu strukturu srži s važnom funkcionalnom ulogom. Uloga strukture četvero-helikalnog snopa najbolje se očituje u sazrijevanju nezrelih čestica srži HBV, koje sadrže kompleks pregenomske RNA/RT. Neuobičajenom reverznom transkripcijom pre-genomske RNA generira se djelomično dvolančana DNA, što je okidač za slijed konformacijskih promjena u dimerima srži. Promjene se najbolje očituju na strukturi četvero-helikalnog snopa dimera gdje osiguravaju izbočivanje hidrofobnog džepa sučelja dimera. Hidrofobni džep tako biva izložen na površini sada zrele srži te osigurava njezinu interakciju s pre-S1 regijom S proteina HBV ovojnice. Ovaj mehanizam osigurava da se samo zrelim česticama srži (s uklopljenom djelomičnom dvolančanom DNA) HBV-a omogućuje uspješna interakcija s proteinima ovojnice, što rezultira virusnim omatanjem i pupanjam s unutarstanične membrane hepatocita.

Abstract (english)

The hepatitis B virus (HBV) is small, enveloped virus, member of the Hepadna viral family with unusual, partially double-stranded DNA genome. The predominant viral core form in vivo is 34 nm particle with T=4 icosahedral symmetry, constructed from 240 copies of the HBV core protein (HBc). The HBV core protein is 22 kD, 183-185 amino acids long protein with primary structure composed of two structurally and functionally distinct regions. The Nterminal region is 149-151 amino acids long assembly domain, capable of directing the correct fold of the core monomer. The 34 residues long C-terminal domain, completely dispensable for core assembly, is extremely rich in conserved arginine (R) residues and takes part in the viral pre-genome/RT binding and encapsidation. The cryo-electron microscopy and X-ray crystallography studies on the HBV core particles revealed an unexpectedly large helical protein structure, with the long α helical hairpin dominating the entire monomer fold. The amphipatic helical hairpins of two core monomers interact forming the compact dimer, whose interface covers the large hydrophobic surfaces of the individual monomers. The hydrophobic interactions thus constitute the major driving force for the dimer assembly and account for the assembled core stability. The four helix bundle of the dimer is a distinct core structural feature, with important functional role. This is well observed upon the maturation of the immature pre-genomic RNA/RT complex-containing HBV core particle. The unusual reverse transcription of the pre-genomic RNA generates the partially ds DNA of mature virion, the event which induces the sequence of the conformational changes in the dimer core protein with which the nucleic acid interacts. The changes are best observable on the fourhelix bundle dimer structure and insure the generating of the dimer hydrophobic pocket on core surface which subsequently interacts with the pre-S1 region of the HBV S envelope protein. This mechanism ensures that only the mature viral core particles (with encapsidated dsDNA) are capable of the successful envelopment and budding at an intracellular hepatocyte membrane.

• Keywords: HBV; proteini virusne ovojnice
• Keywords (english): HBV; envelope proteins
• Language: croatian
• URN:NBN: urn:nbn:hr:217:079010
• Study programme: Title: Molecular Biology; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/prvostupnica (baccalaureus/baccalaurea) molekularne biologije (sveučilišni/a prvostupnik/prvostupnica (baccalaureus/baccalaurea) molekularne biologije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2018-04-10 09:43:22