A complete set of intermolecular potential functions has been developed for use in computer simulations of proteins in their native environment. Parameters are reported for 25 peptide residues as well as the common neutral and charged terminal groups. The potential functions have the simple Coulomb plus Lennard-Jones form and are compatible with the widely used models for water, TIP4P, TIP3P, and SPC. The parameters were obtained and tested primarily in conjunction with Monte Carlo statistical mechanics simulations of 36 pure organic liquids and numerous aqueous solutions of organic ions representative of subunits in the side chains and backbones of proteins. Bond stretch, angle bend, and torsional terms have been adopted from the AMBER united-atom force field. As reported here, further testing has involved studies of conformational energy surfaces and optimizations of the crystal structures for four cyclic hexapeptides and a cyclic pentapeptide. The average root-mean-square deviation from the X-ray structures of the crystals is only 0.17 A for the atomic positions and 3% for the unit cell volumes. A more critical test was then provided by performing energy minimizations for the complete crystal of the protein crambin, including 182 water molecules that were initially placed via a Monte Carlo simulation. The resultant root-mean-square deviation for the non-hydrogen atoms is still ca. 0.2 A and the variation in the errors for charged, polar, and nonpolar residues is small. Improvement is apparent over the AMBER united-atom force field which has previously been demonstrated to be superior to many alternatives. Computer simulations are undoubtedly destined to became an increasingly important means for investigating the structures and dynamics of biomolecular systems.' At the heart of such theoretical calculations are the force fields that describe the interatomic interactions and the mechanics of deformations of the molecules.* There is also little doubt that there will be a continual evolution in force fields with added complexity and improved performance paralleling the availability of computer resources. Our own efforts in this area over the last few years have resulted in the OPLS potential functions for proteins whose development and performance are summarized here. These potential functions have a simple form and they have been parametrized directly to reproduce experimental thermodynamic and structural data on fluids. Consequently, they are computationally efficient and their description of proteins in solution or crystalline environments should be superior to many alterantives that have been developed with limited condensed-phase data. The latter point is pursued here primarily through calculations on the crystal structures for four cyclic hexapeptides, a cyclic pentapeptide, and the protein crambin. Improvements are apparent in comparison to the AMBER united-atom force field3 which has previously been shown to be superior to many alternative^.^ (1) Beveridge, D. L., Jorgensen, W. L., Eds. Ann. N.Y. Acad. Sci. 1986, 482. ( 2 ) For reviews, see: (a) Levitt, M. Annu. Reu. Biophys. Eioeng. 1982, 11, 251. (b) McCammon, J. A. Rep. Prog. Phys. 1984, 47, 1. (3) Weiner, S. J.; Kollman, P. A.; Case, D. A,; Singh, U. C.; Ghio, C.; Alagona, G.; Profeta, S.; Weiner, P. J. Am. Chem. SOC. 1984, 106, 765. Parametrization The peptide residues of proteins contain readily identifiable organic subunits such as amides, hydrocarbons, alcohols, thioethers, etc. In view of this and since data are available on the corresponding pure organic liquids, our approach to developing a force field for proteins was to build it up from parameters demonstrated to yield good descriptions of organic liquids. U1timately, the force field would need to treat both intramolecular terms for bond stretches, angle bends, and torsions, as well as the intermolecular and intramolecular nonbonded interactions. The latter are generally accepted to be the most difficult part of the problem and have been our focus.3 A simple, computationally efficient form was chosen to represent the nonbonded interactions through Coulomb and Lennard-Jones terms interacting between sites centered on nuclei (eq 1). Thus, the intermolecular inter-

The OPLS [optimized potentials for liquid simulations] potential functions for proteins, energy minimizations for crystals of cyclic peptides and crambin.

We present an all atom potential energy function for the simulation of proteins and nucleic acids. This work is an extension of the CH united atom function recently presented by S.J. Weiner et al. J. Amer. Chem. Soc., 106, 765 (1984). The parameters of our function are based on calculations on ethane, propane, n−butane, dimethyl ether, methyl ethyl ether, tetrahydrofuran, imidazole, indole, deoxyadenosine, base paired dinucleoside phosphates, adenine, guanine, uracil, cytosine, thymine, insulin, and myoglobin. We have also used these parameters to carry out the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach.

An all atom force field for simulations of proteins and nucleic acids.

Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.

Multicopper Oxidases and Oxygenases

ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

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Structural and Functional Aspects of Metal Sites in Biology

The synthesis and characterization of μ-η 2 :η 2 peroxo dinuclear copper(II) complexes which to oxyhemocyanin (or oxytyrosinase) in their physicochemical properties are presented. The low-temperature reaction of a di-μ-hydroxo copper(II) complex [Cu(HB(3,5-i-Pr 2 pz) 3 )] 2 (OH) 2 (8) with H 2 O 2 gave a μ-peroxo complex [Cu(HB(3,5-i-Pr 2 pz) 3 )] 2 (O 2 ) (6)

A new model for dioxygen binding in hemocyanin. Synthesis, characterization, and molecular structure of the .mu.-.eta.2:.eta.2 peroxo dinuclear copper(II) complexes, [Cu(HB(3,5-R2pz)3)]2(O2) (R = isopropyl and Ph)

The formation of vibrationally excited heme upon photodissociation of carbonmonoxy myoglobin and its subsequent vibrational energy relaxation was monitored by picosecond anti-Stokes resonance Raman spectroscopy. The anti-Stokes intensity of the nu4 band showed immediate generation of vibrationally excited hemes and biphasic decay of the excited populations. The best fit to double exponentials gave time constants of 1.9 +/- 0.6 and 16 +/- 9 picoseconds for vibrational population decay and 3.0 +/- 1.0 and 25 +/- 14 picoseconds for temperature relaxation of the photolyzed heme when a Boltzmann distribution was assumed. The decay of the nu4 anti-Stokes intensity was accompanied by narrowing and frequency upshift of the Stokes counterpart. This direct monitoring of the cooling dynamics of the heme cofactor within the globin matrix allows the characterization of the vibrational energy flow through the protein moiety and to the water bath.

https://science.sciencemag.org/content/sci/278/5337/443.full.pdf

Direct Observation of Cooling of Heme Upon Photodissociation of Carbonmonoxy Myoglobin

A model for the key intermediate in copper oxygenase reactions, the Cu(II)-OOH complex, was prepared with the novel tripodal pyridylamine ligand, bis(6-pivalamide-2-pyridylmethyl)(2-pyridylmethyl)amine. The HOO- moiety is stabilized by hydrogen bonding to two amine H atoms (see structure on the right).

Teizo Kitagawa

Papers

A new model for dioxygen binding in hemocyanin. Synthesis, characterization, and molecular structure of the .mu.-.eta.2:.eta.2 peroxo dinuclear copper(II) complexes, [Cu(HB(3,5-R2pz)3)]2(O2) (R = isopropyl and Ph)

Direct Observation of Cooling of Heme Upon Photodissociation of Carbonmonoxy Myoglobin

Structural and Spectroscopic Characterization of a Mononuclear Hydroperoxo-Copper(II) Complex with Tripodal Pyridylamine Ligands.

Synthesis and characterization of the dinuclear copper(II) complexes [Cu(HB(3,5-Me2pz)3)]2X (X = O2-, (OH)22-, CO32-, O22-)

Nature of the iron-ligand bond in ferrous low spin hemoproteins studied by resonance Raman scattering.