AF3 _find_template_in_pdb 函数解读

AlphaFold3 中templates模块的_find_template_in_pdb函数用于在 mmCIF 文件中查找与给定模板序列匹配的链，通过三步匹配策略确保找到最佳的模板链。

源代码：

def _find_template_in_pdb(template_chain_id: str,template_sequence: str,mmcif_object: mmcif_parsing.MmcifObject,
) -> Tuple[str, str, int]:"""Tries to find the template chain in the given pdb file.This method tries the three following things in order:1. Tries if there is an exact match in both the chain ID and the sequence.If yes, the chain sequence is returned. Otherwise:2. Tries if there is an exact match only in the sequence.If yes, the chain sequence is returned. Otherwise:3. Tries if there is a fuzzy match (X = wildcard) in the sequence.If yes, the chain sequence is returned.If none of these succeed, a SequenceNotInTemplateError is thrown.Args:template_chain_id: The template chain ID.template_sequence: The template chain sequence.mmcif_object: The PDB object to search for the template in.Returns:A tuple with:* The chain sequence that was found to match the template in the PDB object.* The ID of the chain that is being returned.* The offset where the template sequence starts in the chain sequence.Raises:SequenceNotInTemplateError: If no match is found after the steps describedabove."""# Try if there is an exact match in both the chain ID and the (sub)sequence.pdb_id = mmcif_object.file_idchain_sequence = mmcif_object.chain_to_seqres.get(template_chain_id)if chain_sequence and (template_sequence in chain_sequence):# logging.info(#     "Found an exact template match %s_%s.", pdb_id, template_chain_id# )mapping_offset = chain_sequence.find(template_sequence)return chain_sequence, template_chain_id, mapping_offset# Try if there is an exact match in the (sub)sequence only.for chain_id, chain_sequence in mmcif_object.chain_to_seqres.items():if chain_sequence and (template_sequence in chain_sequence):# logging.info("Found a sequence-only match %s_%s.", pdb_id, chain_id)mapping_offset = chain_sequence.find(template_sequence)return chain_sequence, chain_id, mapping_offset# Return a chain sequence that fuzzy matches (X = wildcard) the template.# Make parenthes