Д¬aspase-3 is activated in the apoptotic cell. CAD release from ICAD inhibition is achieved by cleavage of ICAD at these Asp residues by the caspase-3. ICAD has two caspase recognition sites at Asp117 and Asp224.

Therefore, ICAD has a double function it acts as a CAD inhibitor and also as a chaperone for CAD synthesis assisting the correct assembly of the protein. ICAD is encoded by alternatively spliced mRNAs which generate long (ICAD-L) and short (ICAD-S) forms of ICAD. Per usual in non-apoptotic growing cells caspase activated dnase is held in check inactivated in the cytoplasm thanks to the association with its inhibitor, inhibitor of caspase-activated DNase (ICAD) also known as DNA fragmentation factor 45 kDa (DFF45). DFF45 subunit or ICAD ДFFA is encoded by an alternatively encrypted mRNAs originating two distinct forms: short (ICAD-S) and long (ICAD-L), which act like a specific chaperone ensuring the correct CAD's folding Besides, it contains two aspartic acid residues (Asp117 and Asp224) where CAD is identified and, consequently, it stays bounded until Caspase-3 splits this union. Therefore, a cavity (active site) where DNA can fit is produced, even though there is another binding region responsible for stable DNA complex during its fragmentation. What is more, combining C3вЂ™s amino acids leads to 5 О± helices, 4 ОІ lamina and a loop at the catalytic C-terminal which interact with each other. Moreover, it contains three domains making up a CAD monomer: C1 or N-terminal CAD C2 which conform three separate О± chains and, at last, C3 which is the largest and functionally the most important. Their dissociation allows DFF40 to oligomerize to form a large functional complex which is by itself an active DNase. It remains inactive in growing cells while it is associated with its inhibitor (ICAD, DNA fragmentation factor 45 kDa subunit, DFFA or DFF45) resulting into a complex ICAD-CAD. This heterodimer is an endonuclease with a high content of cysteine residues. Besides, there are other nomenclatures as a result of combining the previous ones. It is also known as caspase activated nuclease (CPAN), dna fragmentation factor 40 (DFF-40), DFF2 and DFFB. Дespite this gene being present in every cell, this protein is only expressed in different tissues and cell variety such as pancreas, heart, colon, leukocytes, prostate, ovary, placenta, kidney, spleen and thymus. Multiple alternatively spliced transcript variants encoding distinct isoforms have been found for this gene, but the biological validity of some variants has not been determined. DFFB has been found to trigger both DNA fragmentation and chromatin condensation during apoptosis. The cleaved fragments of DFFA dissociate from DFFB, the active component of DFF. DFF becomes activated when DFFA is cleaved by caspase-3. DFFA is the substrate for caspase-3 and triggers DNA fragmentation during apoptosis. DNA fragmentation factor (DFF) is a heterodimeric protein of 40-kD (DFFB) and 45-kD ( DFFA) subunits. The apoptotic process is accompanied by shrinkage and fragmentation of the cells and nuclei and degradation of the chromosomal DNA into nucleosomal units. Apoptosis is a cell self-destruct process that removes toxic and/or useless cells during mammalian development and other life processes.

What is icad