Slow-Binding Inhibition of Mycobacterium tuberculosis Shikimate Kinase by Manzamine Alkaloids

TY - JOUR

T1 - Slow-Binding Inhibition of Mycobacterium tuberculosis Shikimate Kinase by Manzamine Alkaloids

AU - Simithy, Johayra

AU - Fuanta, Ngolui Rene

AU - Alturki, Mansour

AU - Hobrath, Judith V.

AU - Wahba, Amir E.

AU - Pina, Ivett

AU - Rath, Jnanendra

AU - Hamann, Mark T.

AU - Deruiter, Jack

AU - Goodwin, Douglas C.

AU - Calderón, Angela I.

PY - 2018/8/14

Y1 - 2018/8/14

N2 - Tuberculosis represents a significant public health crisis. There is an urgent need for novel molecular scaffolds against this pathogen. We screened a small library of marine-derived compounds against shikimate kinase from Mycobacterium tuberculosis (MtSK), a promising target for antitubercular drug development. Six manzamines previously shown to be active against M. tuberculosis were characterized as MtSK inhibitors: manzamine A (1), 8-hydroxymanzamine A (2), manzamine E (3), manzamine F (4), 6-deoxymanzamine X (5), and 6-cyclohexamidomanzamine A (6). All six showed mixed noncompetitive inhibition of MtSK. The lowest KI values were obtained for 6 across all MtSK-substrate complexes. Time-dependent analyses revealed two-step, slow-binding inhibition. The behavior of 1 was typical; initial formation of an enzyme-inhibitor complex (EI) obeyed an apparent KI of ∼30 μM with forward (k5) and reverse (k6) rate constants for isomerization to an EI∗ complex of 0.18 and 0.08 min-1, respectively. In contrast, 6 showed a lower KI for the initial encounter complex (∼1.5 μM), substantially faster isomerization to EI∗ (k5 = 0.91 min-1), and slower back conversion of EI∗ to EI (k6 = 0.04 min-1). Thus, the overall inhibition constants, KI∗, for 1 and 6 were 10 and 0.06 μM, respectively. These findings were consistent with docking predictions of a favorable binding mode and a second, less tightly bound pose for 6 at MtSK. Our results suggest that manzamines, in particular 6, constitute a new scaffold from which drug candidates with novel mechanisms of action could be designed for the treatment of tuberculosis by targeting MtSK.

AB - Tuberculosis represents a significant public health crisis. There is an urgent need for novel molecular scaffolds against this pathogen. We screened a small library of marine-derived compounds against shikimate kinase from Mycobacterium tuberculosis (MtSK), a promising target for antitubercular drug development. Six manzamines previously shown to be active against M. tuberculosis were characterized as MtSK inhibitors: manzamine A (1), 8-hydroxymanzamine A (2), manzamine E (3), manzamine F (4), 6-deoxymanzamine X (5), and 6-cyclohexamidomanzamine A (6). All six showed mixed noncompetitive inhibition of MtSK. The lowest KI values were obtained for 6 across all MtSK-substrate complexes. Time-dependent analyses revealed two-step, slow-binding inhibition. The behavior of 1 was typical; initial formation of an enzyme-inhibitor complex (EI) obeyed an apparent KI of ∼30 μM with forward (k5) and reverse (k6) rate constants for isomerization to an EI∗ complex of 0.18 and 0.08 min-1, respectively. In contrast, 6 showed a lower KI for the initial encounter complex (∼1.5 μM), substantially faster isomerization to EI∗ (k5 = 0.91 min-1), and slower back conversion of EI∗ to EI (k6 = 0.04 min-1). Thus, the overall inhibition constants, KI∗, for 1 and 6 were 10 and 0.06 μM, respectively. These findings were consistent with docking predictions of a favorable binding mode and a second, less tightly bound pose for 6 at MtSK. Our results suggest that manzamines, in particular 6, constitute a new scaffold from which drug candidates with novel mechanisms of action could be designed for the treatment of tuberculosis by targeting MtSK.

KW - Mycobacterium tuberculosis

KW - shikimate kinase

KW - manzamine alkaloids

KW - protein-ligand interactions

KW - mass spectrometry

KW - slow-binding inhibitor

KW - jump dilution experiments

KW - time-dependent inhibition

KW - molecular docking

UR - https://www.scopus.com/pages/publications/85051435425

U2 - 10.1021/acs.biochem.8b00231

DO - 10.1021/acs.biochem.8b00231

M3 - Article

C2 - 30063132

AN - SCOPUS:85051435425

SN - 0006-2960

VL - 57

SP - 4923

EP - 4933

JO - Biochemistry

JF - Biochemistry

IS - 32

ER -