1. Metallo-β-Lactamase
Ian Desmond

2. Overveiw
Metallo-β-Lactamases- enzymes that inactivate β-lactam antibiotics, by catalyzing the hydrolysis of the four-membered ring
no clinically available inhibitors

3. General Structure
Three classes of Metallo-β-Lactamases based on their amino acid sequences: B1, B2, B3
All classes possess:
1) one or two potential Zinc ion binding sites in the active site
2) similar αβ/βα fold

4. Class B1 Broad Spectrum Active with one or two Zn ions in active site
Zn 1 site: 3 Histidine
Zn 2 site: Asparagine-Cysteine-Histidine
Effect of Zn binding: Binding of 2 Zn atoms for optimal hydrolysis
Examples:Bc II, IMP- I, Ccr A, VIM, GIM, SPM-1

5. Class B2 High specificity for hydrolyzing carbapenems
Aeromonas enzymes
Zn 1 site: 2 Histidine, 1 Asparagine
Zn 2 site: Asparagine-Cysteine-Histidine
Effect of Zn binding: Binding of second Zn atom is inhibitory
Catalytic Zn cofactor occupies the Zn 2 site
Examples: Cph A, Sfh-1

6. Class B3 High specifi city for hydrolyzing cephalosporins
Has a Tetrameric enzyme form (LI), all other forms are monomeric
Zn 1 site: 3 Histidine
Zn 2 site: Asparagine-Histidine-Histidine
Effect of Zn binding: Binding of 2 Zn atoms for optimal hydrolysis
Examples: LI, FEZ-1, Gob-1, CAU-1

7. Primary Structure
their primary structures exhibit low degrees of sequence isology
generally less than 43%

8. Secondary Structure two domains of roughly equivalent topology
αβ/βα fold
N-terminal domain=β1β2β3β4β5α1β6α2β7α3 C-terminal domain=β8β9β10β11α4β12α5

9. Secondary Structure

10. Protein Fold

11. Tertiary Structure
Their three-dimensional structures show high degrees of similarity
each domain contains ββββαβα motif.
No significant sequence homology was found between the two motifs.

12. Quaternary Structure
Zn-1 is coordinated to three histidines and a water molecule.
Zn-2 interacts with a cysteine, an aspartic acid, and a histidine (BcII, IMP-1, and CcrA) or an aspartic acid and two histidines (for L1) and two water molecules in a trigonal pyramid.
di-zinc form=one water molecule is bridged between the metal ions.

14. Active Site

15. Structure of Active Site
active site is located at the bottom of a groove running between the two β sheets
The four Zn2+ ligands are arranged in a distorted tetrahedral shape.
Seven out of the nine strictly conserved residues are located in the active site: His88, Asp9O, Leull4, Hisl49, Glyl79, Asnl80 and His210.

16. Works Cited
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