computation of atom radii

src/mol-model/structure/model/properties/utils/accessible-surface-area.ts

-import { ResidueIndex } from 'mol-model/structure';
-import { MoleculeType } from 'mol-model/structure/model/types';
-import { GridLookup3D } from 'mol-math/geometry';
 import { Vec3 } from 'mol-math/linear-algebra';
-import { SortedArray } from 'mol-data/int';
-import { ElementIndex } from 'mol-model/structure/model/indexing';
 import { AtomicHierarchy, AtomicConformation } from '../atomic';
+import { ElementSymbol, VdwRadii } from '../../types';
+import { skipUntil } from 'rxjs/operators';
+import { atomicHet } from 'mol-model/structure/query/queries/internal';
+import { compile } from 'mol-script/runtime/query/compiler';
+
+const defaultNumberOfPoints = 960;
+const defaultProbeSize = 1.4;
+const trigonalCarbonVdw = 1.76;
+const tetrahedralCarbonVdw = 1.87;
+const trigonalNitrogenVdw = 1.65;
+const tetrahedralNitrogenVdw = 1.50;
+/** deviating radii from the definition in types.ts */
+const oxygenVdw = 1.4;
+const sulfurVdw = 1.85;
 
 export function computeModelASA(hierarchy: AtomicHierarchy, conformation: AtomicConformation) {
-    const { lookup3d, proteinResidues } = calcAtomicTraceLookup3D(hierarchy, conformation)
-    const backboneIndices = calcBackboneAtomIndices(hierarchy, proteinResidues)
-
-    const residueCount = proteinResidues.length
-    const numberOfSpherePoints = 960
+    const numberOfSpherePoints = defaultNumberOfPoints;
 
     const ctx: ASAContext = {
-        probeSize: 1.4,
+        probeSize: defaultProbeSize,
         spherePoints: generateSpherePoints(numberOfSpherePoints),
         cons: 4.0 * Math.PI / numberOfSpherePoints,
 
         hierarchy,
-        proteinResidues
-   }
+        conformation
+    }
 
-    calculateASA(ctx)
+    calculateASA(ctx);
 }
 
 function calculateASA(ctx: ASAContext) {
+    console.log(ctx.hierarchy)
+    // 1. extract all heavy atoms
+    // 2. assign radius to all heavy atoms - depends on element
+    // 3. for each residue
+    // 3a. calculate the individual ASA of each atom
+    // 3b. sum up
+    // 3c. (optionally) normalize by maximum value expected for a particular amino acid - needs lookup of max values
+
+    // const { type_symbol } = ctx.hierarchy.atoms;
+    // console.log(type_symbol.value(0));
+
+    const { atoms, residues, residueAtomSegments, derived } = ctx.hierarchy;
+    const { type_symbol } = atoms;
+    const radii: number[] = [];
+
+    // TODO can be more elegant by obtaining residue info once and then using offset to navigate to next residue
+    for (let i = 0; i < type_symbol.rowCount; ++i) {
+        // skip hydrogen atoms
+        if (type_symbol.value(i) === 'H' || type_symbol.value(i) === 'D' || type_symbol.value(i) === 'T')
+            continue;
+
+        // determine group this atom belongs to
+        const groupIndex = residueAtomSegments.index[i];
+
+        // skip entities not part of a peptide chain
+        if (derived.residue.moleculeType[groupIndex] !== 4)
+            continue;
+
+        const atomId = atoms.label_atom_id.value(i);
+        const compId = residues.label_comp_id.value(groupIndex);
+        const element = type_symbol.value(i);
+        radii[radii.length] = determineRadius(atomId, element, compId);
+    }
+}
 
+/**
+ * Gets the van der Waals radius of the given atom following the values defined by Chothia (1976)
+ * J.Mol.Biol.105,1-14. NOTE: the vdw values defined by the paper assume no Hydrogens and thus "inflates" slightly
+ * the heavy atoms to account for Hydrogens. Thus this method cannot be used in a structure that contains Hydrogens!
+ */
+function determineRadius(atomId: string, element: ElementSymbol, compId: string): number {
+    switch (element) {
+        case 'O':
+        return oxygenVdw;
+        case 'S':
+        return sulfurVdw;
+        case 'N':
+        return atomId === 'NZ' ? tetrahedralNitrogenVdw : trigonalNitrogenVdw;
+        case 'C':
+        if (atomId === 'C' || atomId === 'CE1' || atomId === 'CE2' || atomId === 'CE3' ||
+            atomId === 'CH2' || atomId === 'CZ' || atomId === 'CZ2' || atomId === 'CZ3') {
+            return trigonalCarbonVdw;
+        } else if (atomId === 'CA' || atomId === 'CB' || atomId === 'CE' || atomId === 'CG1' ||
+            atomId === 'CG2') {
+            return tetrahedralCarbonVdw;
+        } else if (compId === 'PHE' || compId === 'TRP' || compId === 'TYR' || compId === 'HIS' ||
+            compId === 'ASP' || compId === 'ASN') {
+            return trigonalCarbonVdw;
+        } else if (compId === 'PRO' || compId === 'LYS' || compId === 'ARG' || compId === 'MET' ||
+            compId === 'ILE' || compId === 'LEU') {
+            return tetrahedralCarbonVdw;
+        } else if (compId === 'GLU' || compId === 'GLN') {
+            return atomId === 'CD' ? trigonalCarbonVdw : tetrahedralCarbonVdw;
+        }
+        default:
+        return (VdwRadii as any)[atomId];
+    }
 }
 
+/** Creates a collection of points on a sphere by the Golden Section Spiral algorithm. */
 function generateSpherePoints(numberOfSpherePoints: number): Vec3[] {
-    const points: Vec3[] = []
-    const inc = Math.PI
-
-    return points
+    const points: Vec3[] = [];
+    const inc = Math.PI * (3.0 - Math.sqrt(5.0));
+    const offset = 2.0 / numberOfSpherePoints;
+    for (let k = 0; k < numberOfSpherePoints; ++k) {
+        const y = k * offset - 1.0 + (offset / 2.0);
+        const r = Math.sqrt(1.0 - y * y);
+        const phi = k * inc;
+        points[points.length] = [Math.cos(phi), y, Math.sin(phi) * r] as Vec3;
+    }
+    return points;
 }
 
 interface ASAContext {
@@ -42,54 +120,5 @@ interface ASAContext {
     cons: number,
 
     hierarchy: AtomicHierarchy,
-    proteinResidues: SortedArray<ResidueIndex>
-}
-
-interface BackboneAtomIndices {
-    cIndices: ArrayLike<ElementIndex | -1>
-    hIndices: ArrayLike<ElementIndex | -1>
-    oIndices: ArrayLike<ElementIndex | -1>
-    nIndices: ArrayLike<ElementIndex | -1>
-}
-
-function calcAtomicTraceLookup3D(hierarchy: AtomicHierarchy, conformation: AtomicConformation) {
-    const { x, y, z } = conformation;
-    const { moleculeType, traceElementIndex } = hierarchy.derived.residue
-    const indices: number[] = []
-    const _proteinResidues: number[] = []
-    for (let i = 0, il = moleculeType.length; i < il; ++i) {
-        if (moleculeType[i] === MoleculeType.protein) {
-            indices[indices.length] = traceElementIndex[i]
-            _proteinResidues[_proteinResidues.length] = i
-        }
-    }
-    const lookup3d = GridLookup3D({ x, y, z, indices: SortedArray.ofSortedArray(indices) }, 4);
-    const proteinResidues = SortedArray.ofSortedArray<ResidueIndex>(_proteinResidues)
-    return { lookup3d, proteinResidues }
-}
-
-
-function calcBackboneAtomIndices(hierarchy: AtomicHierarchy, proteinResidues: SortedArray<ResidueIndex>): BackboneAtomIndices {
-    const residueCount = proteinResidues.length
-    const { index } = hierarchy
-
-    const c = new Int32Array(residueCount)
-    const h = new Int32Array(residueCount)
-    const o = new Int32Array(residueCount)
-    const n = new Int32Array(residueCount)
-
-    for (let i = 0, il = residueCount; i < il; ++i) {
-        const rI = proteinResidues[i]
-        c[i] = index.findAtomOnResidue(rI, 'C')
-        h[i] = index.findAtomOnResidue(rI, 'H')
-        o[i] = index.findAtomOnResidue(rI, 'O')
-        n[i] = index.findAtomOnResidue(rI, 'N')
-    }
-
-    return {
-        cIndices: c as unknown as ArrayLike<ElementIndex | -1>,
-        hIndices: h as unknown as ArrayLike<ElementIndex | -1>,
-        oIndices: o as unknown as ArrayLike<ElementIndex | -1>,
-        nIndices: n as unknown as ArrayLike<ElementIndex | -1>,
-    }
+    conformation: AtomicConformation
 }
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