Hello: Surely a naive question: While beginning to treat a multichain, engineered protein - downloaded from PDB web (1.94 A resolution) - with Chimera, I noticed that many amino acids have such feature as GLU 252 below. Same for many SER, ILE, HIS (two imidazole rings for the same residue number) ATOM 2022 N GLU A 252 15.171 -45.532 45.115 1.00 26.12 N ATOM 2023 CA AGLU A 252 14.023 -44.631 45.214 0.50 26.30 C ATOM 2024 CA BGLU A 252 14.048 -44.592 45.252 0.50 26.30 C ATOM 2025 C GLU A 252 13.983 -43.654 44.050 1.00 25.90 C ATOM 2026 O GLU A 252 12.894 -43.403 43.470 1.00 25.36 O ATOM 2027 CB AGLU A 252 13.974 -43.909 46.559 0.50 26.93 C ATOM 2028 CB BGLU A 252 14.170 -43.759 46.533 0.50 26.77 C ATOM 2029 CG AGLU A 252 13.283 -44.741 47.629 0.50 29.02 C ATOM 2030 CG BGLU A 252 12.874 -43.673 47.313 0.50 29.14 C ATOM 2031 CD AGLU A 252 14.088 -45.948 48.051 0.50 33.10 C ATOM 2032 CD BGLU A 252 12.806 -44.716 48.426 0.50 31.91 C ATOM 2033 OE1AGLU A 252 13.481 -47.014 48.330 0.50 34.82 O ATOM 2034 OE1BGLU A 252 13.394 -44.454 49.504 0.50 31.18 O ATOM 2035 OE2AGLU A 252 15.333 -45.828 48.101 0.50 35.49 O ATOM 2036 OE2BGLU A 252 12.162 -45.782 48.231 0.50 33.14 O ATOM 2037 N GLU A 253 15.141 -43.133 43.683 1.00 24.58 N ATOM 2038 CA GLU A 253 15.225 -42.212 42.559 1.00 25.11 C ATOM 2039 C GLU A 253 14.838 -42.941 41.242 1.00 23.83 C ATOM 2040 O GLU A 253 14.142 -42.383 40.374 1.00 23.54 O ATOM 2041 CB GLU A 253 16.637 -41.603 42.476 1.00 26.18 C ATOM 2042 CG GLU A 253 17.033 -40.722 43.697 1.00 30.81 C ATOM 2043 CD GLU A 253 17.635 -41.491 44.915 1.00 36.16 C ATOM 2044 OE1 GLU A 253 17.540 -42.742 45.032 1.00 35.80 O ATOM 2045 OE2 GLU A 253 18.198 -40.809 45.801 1.00 40.87 O About the protein: SOURCE 2 ORGANISM_SCIENTIFIC: PSEUDOMONAS MENDOCINA; SOURCE 3 ORGANISM_TAXID: 300; SOURCE 4 GENE: TMOA; SOURCE 5 EXPRESSION_SYSTEM: ESCHERICHIA COLI; SOURCE 6 EXPRESSION_SYSTEM_TAXID: 562; SOURCE 7 EXPRESSION_SYSTEM_STRAIN: BL21; SOURCE 8 EXPRESSION_SYSTEM_VECTOR_TYPE: PLASMID; SOURCE 9 EXPRESSION_SYSTEM_PLASMID: P58KABE; The said residue are not among those not located in the experiment. I am interested in channels, pores and so on in the protein, so that the above issue is of most concern for me. Thanks for aid francesco pietra