I. Morphology of the hepatitis B virus.
There are three forms of viral particles in the serum of hepatitis B virus-infected patients.
1, large spherical particles, dane particles, consisting of a shell and core, the shell contains HBsAg, glycoprotein-level cell lipids, the core contains the core antigen HBcAg, cyclic double-stranded DNA, DNA polymerase.
2, small spherical particles.
3.Tubular particles. Small spherical particles and tubular particles consist of HBsAg without nucleic acid and are not infectious. Zang Wei, Department of Hepatitis, Weihai Infectious Disease Hospital
Particle structure of HBV
Outer membrane: carries HBsAg
Core shell: carries HBcAg
Core: double-stranded DNA molecules, DNA polymerase.
Note: HBeAg is not in the particle structure.
Difference between serotypes and genotypes of HBV.
The serotype is determined by the amino acid residues of the viral outer membrane protein, the surface antigen, and is the expression of the viral outer membrane protein. HBV is divided into four serotypes based on a common antigenic determinant cluster a and two subtype determinants d/y and w/r on HBsAg: ayw adw ayr adr. w is also divided into w1/w2/w3/w4. q is divided into q+ and q-, making it into nine serotypes. ayw1/ayw2/ayw3/ayw4/ayr/adw2/adw4/adrq+/adrq-/ Although serotyping methods have been established for many years, they are of little clinical significance.
Genetic subtypes are genetic classifications based on genome-wide comparisons, and nucleotide sequence variability ≥ 8% between strains is considered different genotypes. Eight genetic subtypes have been identified, A-H.
Second, the replication process of HBV in the hepatocytes
1, after HBV enters the body, HBsAg enters the host hepatocyte by adhering to the receptor on the surface of the hepatocyte of the susceptible person, and the disease releases the viral core into the cytoplasm.
2, in the cytoplasm, HBV-DNA in a relaxed circular DNA, into the nucleus. In its own DNA-directed DNA polymerase action to extend the positive strand, and the positive strand gap closed, forming cccDNA.
3. Transcription process: cccDNA is used as a template to transcribe the intermediate – pre-genomic RNA (HBV-mRNA). There are four types of HBV-mRNA, including 3.5kb RNA and three subgenomic mRNA. the former carries out viral replication and contains all the genetic information in the DNA sequence of the virus, while the latter is used to synthesize viral proteins (including HBsAg, HBcAg/HBeAg, P protein, X protein, etc.).
4. Reverse transcription process: The pregenomic RNA is transferred to the cytoplasm, where the 3.5kb RNA is wrapped with the P protein together with the nucleocapsid protein to form the viral core. Then reverse transcription into negative-stranded DNA, with the extension of negative-stranded DNA, the pre-genomic RNA is degraded, and the negative-stranded DNA is completely synthesized and the positive-stranded synthesis begins.
5. The newly synthesized double-stranded DNA migrates to the cytoplasmic reticulum tissue and is encapsulated by HBsAg to form the infectious HBV virion and is released outside the cell. Note: Some of the newly synthesized viral cory remains in the cell and enters the nucleus to replenish the cccDNA pool, ensuring a stable storage quantity of cccDNA in the hepatocyte nucleus.
Contact clinical points.
1. Nucleoside analogs act on the process of RNA → double-stranded DNA, i.e. reverse transcription. Reverse transcription is within the viral nucleocapsid, and there is no reverse transcriptase, the DNA polymerase of HBV, in humans. Therefore, the nucleoside analogues acting on reverse transcriptase are not toxic to the human nucleus, but may be mitochondrial toxicity. The mechanism is as follows.
Mitochondria are semi-autonomous organelles that can depend on nuclear DNA to be replicated, transcribed and translated, but they have their own protein synthesis system and can self-synthesize via their own DNA polymerase. DNA polymerase γ is the only polymerase present in mitochondria that is involved in mitochondrial replication, and is therefore also known as mitochondrial DNA (mtDNA) polymerase γ. Nucleoside (acid) analogs may have some effect on mtDNA polymerase γ. The nucleoside (acid) analogs may have an inhibitory effect on mtDNA polymerase γ, leading to a decrease in mtDNA content or even depletion in damaged cells, which affects the oxidative phosphorylation function of mitochondria, resulting in reduced ATP production and cellular dysfunction.
2, Mechanism of action of nucleoside analogues: competitive inhibition of enzymes.