Sources of antibody diversity
There are four main sources of antibody diversity: 1, VH, DH and JH are recombined into functional heavy chains, VL_and VJ(lambda_or_kappa)two chains form functional light chains, light chains are either lambda type or kappa type, and they will not appear on the same antibody at the same time. 2. When VDJ gene is spliced, the diversity of joints is mainly produced in four ways: 1) D gene can be translated into any of the three open reading frames in any direction to produce a total of six possible peptide fragments. 2) During the rearrangement process, hairpin structure will be formed, resulting in the increase or decrease of nitrogen nucleotides, thereby increasing diversity. 3) VDJ connection mechanism, which may add or remove nitrogen nucleotides as part of the VDJ connection process. Sometimes, the coding sequence of several amino acid residues may be lost during recombination. 4) Nitrogen nucleotides can be added or replaced by the activity of terminal deoxynucleotidyl transferase (TdT), especially on either side of the D segment of the VDJ junction of CDR-H3, which constitutes the functional V region. It is estimated that these nitrogen nucleotide changes can lead to CDR-H3 diversity greater than 107, including CDR length ranging from just a few amino acid residues to more than 25 amino acid residues. 3. High frequency mutation of somatic cells.
Category transformation and gene transformation.
Human Antibody Genome Composition
The ligand cells contain the following antibody gene fragments (constant gene segment) encoding antibody light chain and heavy chain C region; 2) light chain V gene fragments (variable gene segment) and J gene fragments (joining segment), which encode light chain variable region; 3) heavy chain V, D gene fragments and C gene fragments (diversity segment), which encode heavy chain variable region. The above gene fragments are located on different chromosomes and distributed in discontinuous clusters.
Antibody gene rearrangement mechanism
Before synthesizing antibody chains, antibody genes must be assembled in the genome of differentiated cells (rearrangements). Fig. 2 shows the overall high level assembly of heavy and light chain genomes and their translation into antibody sequences. Human antibody diversity comes from the assembly of different antibody fragments (VH, DH, JH, Vkappa, Jkappa, Vlambda and Jlambda) and heavy and light chains. The process of human antibody diversification is very complex. It combines with five stages of bone marrow B cell development. Each stage needs to be matched by biochemistry, genetics and cell development.
Flanking sequence-guided gene rearrangement:
V (D) J gene rearrangement is that each gene fragment must be correctly linked, such as V gene fragment and D (heavy chain) or J (light chain) gene fragment, but not other V gene fragments. The recombinant signal sequence (RSS) is a conservative non-coding region located at the point of recombination of V, J, D gene fragments. An RSS consists of conserved heptamers immediately following the coding region, spacing sequences of non-conserved 12 or 23 pairs of bases, and conserved septamers. The interval sequence consisting of 12 or 23 pairs of bases corresponds to one or two pitches in the DNA double helix, so that the heptamer and the ninth polymer are located on the same side of the DNA double helix, which is conducive to gene recombination. Recombination usually occurs in the same chromosome, and the rule of 12/23 is followed. RSS containing 12 pairs of base spacing sequence is only recombined with RSS containing 23 pairs of base spacing sequence. The antibody molecules CDR1 and CDR2 are encoded by V gene fragments, while CDR3 is encoded by recombinant V, J (light chain) or VDJ (heavy chain) gene fragments.
DNA modifying enzymes are commonly involved in V(D)J gene rearrangement:
V (D) J gene recombinant plum identifies the spacer sequence of RSS according to the rule of 12/23, then splits DNA double strands, forms signal link products at the end of the heptamer, and then links head-to-head to form extrachromosomal cyclic DNA, which is lost with cell division. V, (D) and J gene fragments remained on chromosomes were linked to form linkage products.
In addition to the complex mechanism of gene rearrangement, the diversity of antibody libraries also increases the diversity of antibodies, such as high frequency mutations in somatic cells, gene transformation and class transformation.
There is a close relationship between amino acid sequence and antibody function. As we know, even if one amino acid is different, there are huge functional differences between two antibodies with almost the same antibody sequencing amino acid. Therefore, the accuracy of antibody sequencing service is very important in related research.
Other related service:
No comments:
Post a Comment