def merge_all_models_into_first_model(biop_structure):
    """Merge all existing models into a Structure's first_model attribute.

    This directly modifies the Biopython Structure object. Chains IDs will start from A and increment for each new
    chain (model that is converted).

    Args:
        biop_structure (Structure): Structure with multiple models that should be merged

    """
    from string import ascii_uppercase
    idx = 1
    first_model = biop_structure[0]

    for m in biop_structure.get_models():
        # Don't duplicate the original model
        if first_model.id == m.id:
            continue
        for c in m.get_chains():
            c.id = ascii_uppercase[idx]
            first_model.add(c)
        idx += 1
Merge all existing models into a Structure's first_model attribute.

    This directly modifies the Biopython Structure object. Chains IDs will start from A and increment for each new
    chain (model that is converted).

    Args:
        biop_structure (Structure): Structure with multiple models that should be merged