Dynamic Mechanisms of Neutral Amino Acid Exchanger ASCT2 Transporting Substrate Glutamine

Tumor cells rely on the high expression of transporter
proteins
to meet their nutrient demands, with alanine-serine-cysteine transporter
2 (ASCT2) being a key player in glutamine (Gln) uptake. Glutamine,
a conditionally essential amino acid abundant in protein-rich foods,
such as meat, dairy, and legumes, serves as a critical nitrogen and
carbon source for cellular biosynthesis. ASCT2-mediated Gln transport
not only fuels cancer progression but also plays a role in nutrient
absorption in healthy tissues, particularly the gut, where dietary
amino acids are assimilated. Despite its dual significance in physiology
and pathology, the molecular mechanisms of Gln transport by ASCT2
remain poorly understood, hindering the development of targeted therapies
and dietary interventions. In this study, microsecond classical and
Gaussian accelerated molecular dynamics (CMD/GaMD) were conducted
to investigate the dynamic mechanism of glutamine transportation by
ASCT2. A Markov State Model (MSM) was built based on the enhanced
sampling trajectories to search for the communication pathways and
critical transition states during the allosteric movement of helical
hairpin 2 (HP2), a structural gatekeeper of transport. Additionally,
the C467R mutation was found to disrupt HP2 dynamics, impair Gln binding,
and hinder Gln transport. Intriguingly, substrate-bound ASCT2 exhibited
prolonged HP2 opening compared to its unloaded state, suggesting that
food-derived Gln may stabilize transporter conformations. The important
transition states of the transporter opening process were also identified
from the MSM. The key pathway from the “close” to “open”
state is S2 → S15 → S10 → S6 → S5 →
S7 → S19, with a maximum probability of 16.76%. These findings
not only advance ASCT2-targeted drug discovery but also offer a framework
for designing functional foods or nutraceuticals that modulate amino
acid bioavailability, potentially leveraging natural compounds to
fine-tune ASCT2 activity for cancer prevention or metabolic health
optimization.