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Structural insights into the substrate-binding proteins Mce1A and Mce4A from Mycobacterium tuberculosis

DOI: 10.1107/S2052252521006199 DOI Help

Authors: Pooja Asthana (University of Oulu) , Dhirendra Singh (University of Oulu) , Jan Skov Pedersen (Aarhus University) , Mikko J. Hynonen (University of Oulu) , Ramita Sulu (University of Oulu) , Abhinandan V. Murthy (University of Oulu) , Mikko Laitaoja (University of Eastern Finland) , Janne Jänis (University of Eastern Finland) , Lee W. Riley (University of California, Berkeley) , Rajaram Venkatesan (University of Oulu)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Iucrj , VOL 8

State: Published (Approved)
Published: September 2021
Diamond Proposal Number(s): 14794

Open Access Open Access

Abstract: Mycobacterium tuberculosis (Mtb), which is responsible for more than a million deaths annually, uses lipids as the source of carbon and energy for its survival in the latent phase of infection. Mtb cannot synthesize all of the lipid molecules required for its growth and pathogenicity. Therefore, it relies on transporters such as the mammalian cell entry (Mce) complexes to import lipids from the host across the cell wall. Despite their importance for the survival and pathogenicity of Mtb, information on the structural properties of these proteins is not yet available. Each of the four Mce complexes in Mtb (Mce1–4) comprises six substrate-binding proteins (SBPs; MceA–F), each of which contains four conserved domains (N-terminal transmembrane, MCE, helical and C-terminal unstructured tail domains). Here, the properties of the various domains of Mtb Mce1A and Mce4A, which are involved in the import of mycolic/fatty acids and cholesterol, respectively, are reported. In the crystal structure of the MCE domain of Mce4A (MtMce4A39–140) a domain-swapped conformation is observed, whereas solution studies, including small-angle X-ray scattering (SAXS), indicate that all Mce1A and Mce4A domains are predominantly monomeric. Further, structural comparisons show interesting differences from the bacterial homologs MlaD, PqiB and LetB, which form homohexamers when assembled as functional transporter complexes. These data, and the fact that there are six SBPs in each Mtb mce operon, suggest that the MceA–F SBPs from Mce1–4 may form heterohexamers. Also, interestingly, the purification and SAXS analysis showed that the helical domains interact with the detergent micelle, suggesting that when assembled the helical domains of MceA–F may form a hydrophobic pore for lipid transport, as observed in EcPqiB. Overall, these data highlight the unique structural properties of the Mtb Mce SBPs.

Journal Keywords: Mycobacterium tuberculosis; mammalian cell entry proteins; Mce1; Mce4; substrate-binding proteins; lipids; ABC transporters; crystal structure; SAXS; membrane proteins; protein structure; X-ray crystallography

Diamond Keywords: Tuberculosis (TB); Bacteria

Subject Areas: Biology and Bio-materials

Instruments: B21-High Throughput SAXS

Other Facilities: BioMax at MAX IV; ESRF

Added On: 02/08/2021 11:53


Discipline Tags:

Pathogens Infectious Diseases Health & Wellbeing Structural biology Life Sciences & Biotech

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)