54 segments mutations

FIGURE 5.3.9 Human antibodies must be immensely diverse to antieipate the unpredictable infections that beset us. The variable regions on the two arms of antibodies include three hypervariable segments (dark stripes) that bind directly to invaders. These segments mutate much more than other parts of antibodies variable regions. (From Caporale, L.H., Am. Sci., 91, 234, 2003. With permission.)... 

Pseudogene An inactive segment of DNA arising by mutation of a parental active gene. 

Figure 41-17. Diagram of the structure of the CFTR protein (not to scale). The protein contains twelve transmembrane segments (probably helical), two nucleotide-binding folds or domains (NBFl and NBF2), and one regulatory (R) domain. NBFl and NBF2 probably bind ATP and couple its hydrolysis to transport of Cl . Phe 508, the major locus of mutations in cystic fibrosis, is located in NBFl.

Figure 48-15. Simplified scheme of the causation of achondroplasia (MIM 100800). In most cases studied so far, the mutation has been a G to A transition at nucleotide 1138. In a few cases, the mutation was a G to C transversion at the same nucleotide. This particular nucleotide is a real "hot spot" for mutation. Both mutations result in replacement of a Gly residue by an Arg residue in the transmembrane segment of the receptor. A few cases involving replacement of Gly by Cys at codon 375 have also been reported.

The notion that the segment containing C3 and T3 is important for conformational adaptability of the protein is supported by mutations in yeast. Mutations of the genes of the H-ATPase of Saccharomyces cerevisiae resulted in a thermo-sensitive... 

Fig. 3. (A) Model of the proposed pore forming part of K channel subunits. Segments S5 and S6 are possibly membrane-spanning helices. The helices are connected by a hydrophobic segment H5 which may be tucked into the lipid bilayer [48]. H5 is flanked by two proline residues P. Adjacent to these proline residues are amino acid side chains ( ) important for external TEA binding [45,46]. Approximately halfway between these two proline residues are amino acid side chains ( ) affecting internal TEA binding [46,47] and K channel selectivity [48]. (B) Mutations are indicated which affect in Shaker channels external TEA (TEAe) or internal TEA (TEA,) binding. Concentrations of TEA for half block of the wild-type and mutant K channels are given at the right-hand side of the corresponding sequence. Data have been compiled from [45-47].

Somatic hypermutation High frequency of mutation that occurs in the gene segments encoding the variable regions of antibodies during the differentiation of B lymphocytes into antibody-producing plasma cells. 

---