Human adenylate kinase 4 structure and function of
May 5th, 2012Adenylate kinase is widely present in the biological body, involved in intracellular energy and nucleotide metabolism. They are reversible catalytic phosphate transfer reaction, the γ-phosphate triphosphate adenylate or guanylate monophosphate adenylate, the reaction requires magnesium ions auxiliary. Adenylate kinase belongs to the monophosphate nucleotide kinase family, the family also includes the guanylate kinase, thymidine kinase, and birds pyrimidine \ cytosine kinase. All of these enzymes have common typical alpha \ beta fold, including α-helix surrounded by a core β-sheet, the N-terminal common phosphate binding P-loop. Adenylate kinase consists of three domains: the CORE domain of LID domain, and a single combination of phosphoric acid adenylate NMPbind domain. Adenylate kinase based on the length of the LID domain is divided into long-subtype and short subtype. Short LID structure of the subtypes of adenylate kinase domain by a flexible ring, LID long subtype of adenylate kinase domain is composed of four anti-parallel sheets. AK4 is found in the AK family in only one special member of the AK catalytic activity, AK4 of physiological functions, as well as inactivation of the reasons still unknown. Therefore, this paper conducted a comprehensive study of the AK4 the structure and function and catalytic mechanism.AK4 in Gln159 can not like the other AK Arg interacts with the transfer of phosphate groups to form hydrogen bonds stabilize the reaction intermediate state, like other AK phosphate transfer reaction can not occur in the AK4, which is why the mother AK4, whether activity in experiments in vitro or in vivo mutation complementation experiments did not show any AK activity. AK4 did not show the catalytic activity of AK to have the AK catalytic activity and other experimental results can be seen from the AK4 GP5 of crystal structure, and AK4 (Q159R) mutant, however, the AK4 itself also has a substrate binding ability. AK4 (Q159R) mutants to GTP on the phosphate group transfer to AMP, AK4 can be combined with GTP, AMP, GDP and ADP nucleotide. Therefore, because of the involvement of the catalytic phosphate transfer of important amino acids Arg Gln replaced by the mother the AK4 not AK catalytic activity, but still has the ability to nucleotide binding, we can speculate, AK4 in the body can play a role as a carrier of the nucleotide.
Through the detection of AK4 of mRNA and protein levels, we found that The AK4 the expression levels of cellular stress, such as Hypoxia exists under will rise sharply. Therefore the AK4 there may be the cellular stress response protein expression in the cell there is no pressure to rise. AK4 the end of the high expression levels of HEK293 cells AK4siRNA experiments show that the the AK4 siRNA in HEK293 cells growth, morphology, survival, have a great impact, with AK4 expression of the degree of inhibition increased the greater the impact; and AK4 protein expression is suppressed will lead to HEK293 cells is difficult to form clones. It can be seen, growth and developmental processes of AK4 in HEK293 cells is very important. AK4 in the background expression of AK4 protein experiments showed that overexpression of low levels of cell SH-SY5Y, under the microscope, over-expression of the form and density of of AK4 the SH-SY5Y cells with the control group did not differ significantly; MTT to measure the cell activity experiments further evidence that overexpression of AK4 SH-SY5Y survival rate did not significantly affect However, in the case of cellular stress (H 2 O 2 treatment), AK4 expressing cells than control cells survival, in other words, AK4 over-expression can protect SH-SY5Y cells against H2O2-induced cell death. The above results can be seen, AK4 may be a cellular stress response protein, the AK4 the expression on cell growth and development is very important, and AK4 expression of the protective effect on cells from This article further study the possible mechanism AK4 to play a role in the body, we are trying to find the AK4 interaction of the protein. AK4-FLAG immune co-precipitation and mass spectrometry analysis of the inner mitochondrial membrane protein ANT may be involved in the interaction of AK4, and then the reverse co-immunoprecipitation experiments to further determine the interaction of AK4 and ANT. The ANT and AK4 in the case of the cell to face oxidative stress, the interaction will be enhanced, we speculated that The ANT and AK4 interaction may be involved in the process AK4 protected cells under oxidative stress.To further understand the AK4 and other protein interactions by in vitro expression and purification of human source of AK4, as well as the AK4 sequence is highly similar to AK3 the His tag fusion protein, a His pull-down experiments in vitro. Vitro His-taggedpull-down to further define the interaction between AK4 and ANT, but also found AK4-interacting protein ATP synthase F1 complex of alpha and beta subunits.
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