S1d1-3 Control of Regioselectivity of Heme Oyxgenase by Reconstruction of Hydrogen-Bonding Interactions between Substrate and Enzyme(S1-d1: "Structure and Function of Weak Interactions in Protein Molecules",Symposia,Abstract,Meeting Program of EABS & BSJ 2006)

Hiroshi Fujii
2006 Seibutsu Butsuri  
Regioselectivc reactions catalyzed by enzymes are very impertant biologically ancl chernically. Therefore, rnelecular meehanisms of regioseleetive reactions have been studied fbr varinus enzymes wirh various spectroscopic methods. wr h"ve studied the moleculaT mechanism of heme eKygenase (HO), which catalyzes rcgiosclcetivc dcgradaLiun ol' hcmc (iron pretupurphyrinlX) tu u-biliverdin, CO, and frce iren ion, We have found twe csscntial amine acid rcsidves, in rat-HO. for the a-tegioselective
more » ... degradation. INle shDwed that the Asp-140 ancl Arg-IS3 residues control oxygen activation process and the substate (heme) binding ptocess via hyclrogen-bunding interaetions, respectively. With combination ol' the Asp-140 and Arg-183 rcsiducs, Lhe u-meso positiun ot' the hemc is placed at the ncarest pesition from the activatcd exygen spccics. resulting in the a-regioselectlve reaction. This mechanism let us iniagine that we can switch the regioseTectivity of HO if we can controt an orientation of the heme in HO so thAt the other meso pesitien is placed ut the nearest position fbom the activated oxygen species. To realize this idea, on thc basis of the cr}Tstal structurc of the wilcl type HO, we desi.uned u mutarit. in which the other meso position is placed ut the iieaTest position fu)m the actiyated t)xygen species. In this presentation. we wilt show o"r strutegy for controlling the orientation of the heme and regioselectivities ei the mu tants prepared according Lo the strategy, of Nuclcar Physics, China Institute of Atomic Encrgy, iSchoel of Science, Hebei Universiry of Tlechnology 31]he Key [.aboratory of Beam IbchnologyuiidModificationofMinistryefEducatien.BeijingNormalUniversity The double strand breaks (DSBs} of DNA arc consj clcred Lo bu thc mest impoTtant initial damagc of all bie]ogicat cffects induccd by radiation. Hcavy ions with high LET can deposit rnore energy in niedium and have cornplex track structure. It is especially neeessary to iiivestigate the DNA damuge induced by hettvy ion, Using iLi oi 19McV (LET=120kcViym, in aqueous solution) and i7C oi 84MeV {LET=Z40keVlpm) generated by HI-13 tanden] accelerator of China Institute of Aternic Encrgy (CIAE), three conditions of pUCt9 plasmid DNA samplcs including aguiform, dry and adding ftee radicaS scavenger (rnannitol) with various concentrtttiens are irTadiated at different doses ffom 10 to 1000Gy in utmosphere environment. Atter irradiaimg, thcsc DNA samplcs arc anaLyzed with atoinic forcc microscopy (AFM) and the gel electrophoresis. The ehanges of three forms ef DNA, supercoited (intact DNA), open circular (O(].DNA with SSB) and linear form {L,DNA with DSB), us the dose are observed, The distribution functien of DNA fragincnt lcngth is gaincd by thc AFM direet obscrvation of thc DNA fragments, ln order to evaluate the relative biological effbctivcness (RBE) of DNA dun]age induced by heayy iolls. pUCI9 p}asmid DNA is irradiated also by T rays. Thus the dese and LET dependence on the DSBs induced and protection functien er the free radical scuvenger are obtained. The direet und indireet interactioms of heavy ion witl} different DNA samples are estiirrate. Using thc randorn breakage rnodel the length distribution ef short J)NA fragments induced by 'Li iens i$ analyncd. From the dynamical ana]ysis of a motor protcin (kincsin) we found that motor protein could change thc atnplitudc of thc lntrarnoleeulaT interaction in a largc range corresponding to different water pepuiatiolls uroulld. I4ig make a simple calculation fer the clectrostatic intoractien cncrgy bctwccn twe ehargcd residues at two different hydratioll states to give a quantitative description about how 1arge the change of the energy could he. At the hack door of the catalytic site of kilesin there is a 'latch' rormed by a pair of oppositely charged residues, R216 und E2S3. During a pcriod et' catalysis the distancc betwecn the two rcsiducs changcs frem O.4nm to O.9nm, which ce[respond to the close aiid ppen states of the back deor respectivety. To calclllate the e]ectrostatic energy we must detenmine what dielecnic collstants could be used for the two cases. For bulk water the dielectric constant is 8e, However, for the water forming the hydration shell, which is about e.4 nm thick, the dielectric constant is S. With these values we calculated the electrostutic energy fer the close st"te as 70 kJtmel and that fov the opell state as 2 kJimei, These twe values are of reasc}nable orders sinee the former is 1arge en[iugh for closing thc baek deer against thermal disturbs and thc laiter is ot' thc same orck;r as that of the thermal motion energy. This result shows that dLECcrcnt water popuLations may result in large change for weak inteructions and pretein could make use of this special funcLio" of water to irnplement important confeiniatienut changes, Sldl-6 A Statistical Model on the Protein-Water Network due to Hydrogen BondsOHai-JanWang"i,Xlao-ZhengHong",Xin-WUBa' 'Coll. of Chcmistry and Enviromental Scicncc, Hebei Univ., 2Tntcr Centct for Matcrial Physics, Chin. Acad. of Sei., 'Coll. of Physical Scicence and Tecnologe. Hcbei Univ. Bascd on a statistical thcory propesed on a single eomponent hydrogcn bonding(HB) system, we eensider the relevant properties of the netwark of protein and water inolecu]es duc to hydrogcn bonds. For thc protein-wateT systems, we ps}int out that, whieh cun undergo a sol-gei phase transition process svith the currcsponding critical cendition alld thc scaling laws aie ebtained. in dctai1, wc derive the eguilibrium free energy anid the cluster size distribution of the preteinwater system. 1n addition, by rneans of an invariamt pToperty of tbe siie disnibution, we found the sol-gel transhinn is a kind of geometricat phase transition. Furthermure, sume statistical parameters that are closely related to elastic properties of thc protein-watcr nctwotk are caniod out, which includc the n"mber of the effectiye cross-linkages. the numbers of elastic active chaills and dangling ehains as -,el] us the mers ef them. Final, u numerical cuLculation un these paramcters is presentcd for a modclcd systcm,
doi:10.2142/biophys.46.s107_1 fatcat:xnrjhfqfjbggpainyznolpybf4