Radoux et al. present a computational workflow that calculates grid-based atomic propensities (SuperStar) for donor, acceptor, and hydrophobic probes, weights them by cavity buriedness (LIGSITE), then samples the weighted maps with three simple molecular probes to produce separate donor, acceptor, and apolar hotspot maps from apo protein structures alone . Prior methods either locate generic atomic hotspots (GRID, SuperStar) or consensus sites (FTMap, MSCS) but do not identify which specific interactions drive fragment binding from a global apo search. This gap is the paper's central novelty .
On 21 fragment–lead pairs across 15 proteins, fragment atoms rank at a median of 97% while lead atoms (outside the fragment core) rank at 72%, demonstrating the maps preferentially locate fragment cores rather than merely binding sites . Heuristic contour levels of 14 and 17 (derived from the dataset's upper quartile median) successfully isolate binding-site interactions from a global search in most cases.
Detailed analyses of Protein Kinase B and pantothenate synthetase show that group efficiency (GE) patterns correlate with hotspot map scores—e.g., a chloro group placed in a highly scoring apolar region is the most group-efficient addition . A notable observation: polar interactions predicted by the maps are frequently left unsatisfied by fragments but satisfied by transition-state analogues, providing a spatial illustration of Hann's complexity constraint .
Strengths: Fast (minutes, no MD), unbiased global search from apo structures, directly actionable visual output for medicinal chemists, and retrospective quantification against an independent fragment–lead dataset.
Limitations: The validation set of 21 pairs is modest and drawn from a single collation, raising selection-bias concerns . The 14/17 thresholds are dataset-derived heuristics whose generality is untested. Conformational changes like the p38α DFG-out pocket are invisible to apo-based maps—a limitation the authors acknowledge . Water-mediated interactions are excluded by default (recoverable only if explicitly included), and no prospective blind test on targets outside the training set is presented. UCB (a pharma company) co-funded the work but no explicit conflict-of-interest statement appears in the text .
An independent, larger dataset showing fragment atoms ranking randomly (~50%) on apo-derived maps, or thresholds 14/17 failing to discriminate binding from non-binding pockets across diverse targets, would undermine the central claim. Additionally, if ensemble-based calculations showed no improvement over single-structure maps, the proposed future direction would lack merit.
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