Words similar to crystallographically
Example sentences for: crystallographically
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The data for both rabbit and yeast Hint enzymes indicate that the dimer's two crystallographically defined nucleotide-binding sites [ 25] bind nucleotide independently and fit well to a single submicromolar K m for each enzyme (Figure 2) [ 30].
These estimates are in excellent agreement with the crystallographically determined secondary structure of ~40% α-helix and 30% β-structure [ 37 ] . Metal analyses on multiple preparations of wild-type L1 demonstrated that the enzyme binds 1.9 ± 0.2 Zn(II) ions per monomer (Table 2), in agreement with previous results [ 36 ] .
The substrate-binding model showed that Tyr228 in L1 was position-conserved with Asn233 in the other crystallographically characterized metallo-β-lactamases [ 37 42 44 45 46 ] . Spencer and coworkers postulated that Tyr228 is part of an oxyanion hole that interacts with the β-lactam carbonyl on substrate and helps to stabilize the putative tetrahedral intermediate formed during substrate turnover [ 37 ] . To test this hypothesis, Tyr228 was changed to an alanine and to a phenylalanine to afford the Y228A and Y228F mutants, respectively.
All crystallographically characterized metallo-β-lactamases have a flexible amino acid chain that extends over the active site [ 37 42 44 45 46 47 48 49 ] . Previous NMR studies on CcrA have shown that this loop "clamps down" on substrate or inhibitor upon binding, and there is speculation that the distortion of substrate upon clamping down of the loop may drive catalysis [ 50 ] . The crystal structure of L1 showed that there is a large loop that extends over the active site, and modeling studies have predicted that two residues, Ile164 and Phe158, make significant contacts with large, hydrophobic substituents at the 2' or 6' positions on penicillins, cephalosporins, or carbapenems [ 37 ] . To test this prediction, Ile 164 and Phe158 were changed from large, hydrophobic residues to alanines to afford the I164A and F158A mutants.
Instead, we predict that the insertion of an aspartic acid into the active site at position 224 results in a change in the hydrogen bonding network in L1; this hydrogen bonding network is extensive in all metallo-β-lactamases that have been characterized crystallographically [ 37 42 44 45 48 49 62 63 ] . The N233D mutant also exhibited greatly reduced k cat values for biapenem and meropenem but not for imipenem or any of the other substrates tested.
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