Conformational sampling of the botulinum neurotoxin serotype A light chain: implications for inhibitor binding.
Botulinum neurotoxins (BoNTs) are the most potent of the known biological toxins, and consequently are listed as category A biowarfare agents. Currently, the only treatments against BoNTs include preventative antitoxins and long-term supportive care. Consequently, there is an urgent need for therapeutics to counter these enzymes--post exposure. In a previous study, we identified a number of small, nonpeptidic lead inhibitors of BoNT serotype A light chain (BoNT/A LC) metalloprotease activity, and we identified a common pharmacophore for these molecules. In this study, we have focused on how the dynamic movement of amino acid residues in and surrounding the substrate binding cleft of the BoNT/A LC might affect inhibitor binding modes. The X-ray crystal structures of two BoNT/A LCs (PDB refcodes=3BTA and 1E1H) were examined. Results from these analyses indicate that the core structural features of the examined BoNT/A LCs, including alpha-helices and beta-sheets, remained relatively unchanged during 1 ns dynamics trajectories. However, conformational flexibility was observed in surface loops bordering the substrate binding clefts in both examined structures. Our analyses indicate that these loops may possess the ability to decrease the solvent accessibility of the substrate binding cleft, while at the same time creating new residue contacts for the inhibitors. Loop movements and conformational/positional analyses of residues within the substrate binding cleft are discussed with respect to BoNT/A LC inhibitor binding and our common pharmacophore for inhibition. The results from these studies may aid in the future identification/development of more potent small molecule inhibitors that take advantage of new binding contacts in the BoNT/A LC.
Burnett
James C
JC
Developmental Therapeutics Program, NCI Frederick, Frederick, MD 21702, USA.
Schmidt
James J
JJ
McGrath
Connor F
CF
Nguyen
Tam L
TL
Hermone
Ann R
AR
Panchal
Rekha G
RG
Vennerstrom
Jonathan L
JL
Kodukula
Krishna
K
Zaharevitz
Daniel W
DW
Gussio
Rick
R
Bavari
Sina
S
D019274:Botulinum Toxins, Type A / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D007546:Isoquinolines / Q000737:chemistry; D045726:Metalloproteases / Q000037:antagonists & inhibitors; D008958:Models, Molecular; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits; D011804:Quinolines / Q000737:chemistry; D012834:Silver / Q000737:chemistry; D013329:Structure-Activity Relationship
D007546:Isoquinolines; D009281:Naphthalenes; D021122:Protein Subunits; D011804:Quinolines; C072235:michellamine A; D012834:Silver; D045726:Metalloproteases; D019274:Botulinum Toxins, Type A