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N-terminal Proline Receives Wrong sp³ Secondary Amine Hybridization #40

@TKanX

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@TKanX

Description:

ops::hydro::construct_n_term_hydrogens treats every N-terminal protein residue as a primary amine, ignoring that PRO's backbone nitrogen is a secondary amine (N–CA + N–CD). For any structure where PRO occupies the N-terminus, this over-places hydrogens by +1 in both protonated and neutral conditions and distributes them without constraining the N–CD ring bond direction.

Tasks:

  • Branch on residue.standard_name == Some(StandardResidue::PRO)
  • Resolve CD via residue.atom("CD") and construct H positions from the N–CA and N–CD vectors (anti-bisector + cross-product tetrahedral geometry)
  • Protonated PRO: place H2 + H3; neutral PRO: place H2 only

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