# Mechanistic profiling and optimized production of Altenusin, a fungal carboxy-biphenyl scaffold for tyrosinase inhibition

## TL;DR

This paper explores Altenusin, a fungal compound, as a potential inhibitor of tyrosinase, an enzyme involved in skin pigmentation and food browning.

## Contribution

The study introduces a workflow combining structure-based screening, fermentation optimization, and mechanistic analysis to evaluate Altenusin as a tyrosinase inhibitor scaffold.

## Key findings

- Altenusin inhibits tyrosinase with IC50 values of 0.381 mM (l-tyrosine) and 0.162 mM (l-DOPA).
- Fermentation optimization increased Altenusin production to 0.254 g L−1.
- Altenusin exhibits radical-scavenging and copper-reducing activity with moderate Cu2+ chelation.

## Abstract

Tyrosinase is a binuclear copper oxidase central to melanogenesis and food browning and is a major target for depigmenting and anti-browning agents. Here we evaluate Altenusin, a fungal carboxy-biphenyl polyketide, as a tyrosinase-inhibitor scaffold by combining structure-based screening, enhanced fermentation and mechanistic enzymology. Docking against the mushroom tyrosinase Agaricus bisporus PPO3 (AbPPO3) highlighted Altenusin as a presumed dicopper-site binder, and genome mining of the producer strain revealed a polyketide synthase gene cluster consistent with its biosynthesis. Fermentation optimization and bioreactor transfer increased Altenusin titers up to 0.254 ± 0.022 g L−1. In vitro, Altenusin inhibited in a substrate-dependent manner, with IC50 values of 0.381 ± 0.002 mM (l-tyrosine) and 0.162 ± 0.023 mM (l-DOPA); kinetic analysis indicated competitive monophenolase inhibition and mixed-type diphenolase inhibition. Altenusin also showed strong radical-scavenging and copper-reducing activity, moderate Cu2+ chelation and a narrow cytotoxicity window in HepG2 cells (48 h, CC50: 0.093 mM). Overall, these data define Altenusin as a biotechnologically tractable starting point for fungal carboxy-biphenyl inhibitor discovery.

An integrated upstream/downstream-to-mechanism workflow supports altenusin as a scalable, assay-robust tyrosinase-inhibitor scaffold for anti-melanosis strategies.