No abstract

The regulation of human mitochondrial NAD(P)+-dependent malic enzyme (m-NAD-ME) by ATP and fumarate may be crucial for the metabolism of glutamine for energy production in rapidly proliferating tissues and tumors. Here we report the crystal structure at 2.2 A resolution of m-NAD-ME in complex with ATP, Mn2+, tartronate, and fumarate. Our structural, kinetic, and mutagenesis studies reveal unexpectedly that ATP is an active-site inhibitor of the enzyme, despite the presence of an exo binding site. The structure also reveals the allosteric binding site for fumarate in the dimer interface. Mutations in this binding site abolished the activating effects of fumarate. Comparison to the structure in the absence of fumarate indicates a possible molecular mechanism for the allosteric function of this compound.

Localized tracheobronchial amyloidosis is a rare disease that results from submucosal deposition of insoluble amyloid proteins in the large airways. Amyloidosis affecting the larynx and subglottic space typically results in unilateral, nodular vocal cord infiltration. It rarely can present with bilateral vocal cord involvement and can progress to lifethreatening respiratory failure due to upper airway obstruction. In these patients, typical treatment modalities such as CO2 laser ablation are often ineffectual. Bronchiectasis is a predisposing risk factor associated with the secondary (AA) form of disease. We present a patient with the primary (AL) form of localized laryngotracheal amyloidosis with pre-existing bronchiectasis, and also review the existing literature on this disease.