Chronic Disease Notes

By the end of this lecture series, students will:

Understand general principles of metallobiology, emphasizing metal types and their incorporation in biological systems, leading to downstream effects.
Understand the relationship between metals and disease, focusing on Wilson’s disease (copper overload), Menkes disease (copper deficiency), and Haemochromatosis (iron overload).

Cells need mechanisms to ensure the correct metal reaches the right protein.
Dehydratases contain an $[4Fe-4S]$ cluster at the active site (e.g., aconitase, fumarase).
Fumarase catalyzes the hydration of fumarate to malate in the citric acid cycle.
Increasing copper concentration leads to iron loss from fumarate (experimental example).

Cells must have mechanisms to ensure the correct metal gets to the right protein.
Human pathogenic fungi (soil, trees) produce spores.
Macrophages deal with fungal spores; immunocompromised patients may have issues with fungal growth.
Example: Brain section with yeast infection.
Blood-brain barrier (BBB) penetration is dependent on urease activity.
Experiment: Cobalt replaces nickel, showing yeast penetration. Cobalt can displace nickel due to larger concentrations outcompeting metals higher in the Irving Williams series.

Ferrochelatase catalyzes the insertion of iron into protoporphyrin IX.
Zinc protoporphyrin forms in patients with anemia, leading to loss of activity/function.
Cryptococcal Urease - loss of function.

Mechanisms are needed for each biological metal to:
- Sense how much metal is in the cell and how much is needed.
- Distribute metal to the correct location.
- Store, export, or prevent uptake of excess metal.
Aim: Ensure that metal need is met and any free cellular metal does not cause oxidative stress or inhibit protein function.
Distribute within the cell, import, and export.

Many microbial metal-sensing transcription factors exist.
Metal binding causes an allosteric change.
Binding sensitivity increases as you move up the Irving Williams series, meaning the transcription factors are more sensitive (Bacterial copper sensitivity to one atom).
Transcription factors act as sensors.

Aft1 and Aft2 regulon is switched off when iron is replete and switched on when iron is depleted.
Several proteins are involved including Fra1, Fra2, Grx3/4, Atm1, Msn5 and Yap5
Under iron deplete conditions, iron uptake genes (Fit1-3, Arn1-4, Ftr1, Fet3 Fre1/2) are activated along with CTH2, iron-sulfur cluster proteins, heme biosynthesis, iron storage, respiration, TCA cycle, and other essential iron-requiring proteins and processes.

Binding of copper inactivates Mac1, unlike other allosteric binders.
CTR1 is a copper transporter.
Yeast needs copper to survive DNA damage.
MethylMethaneSulfonate (MMS) is a DNA damaging agent that methylates N7-guanine residue.

ZIP transporters are degraded in the presence of high concentrations of iron in the cytosol, while at low concentrations of zinc, the protein is endocytosed and cleaved, returning to the membrane.
Hepcidin regulates Ferroportin (FPN) release and regulates iron in the cell, internalizing the transporter.

Chaperones are involved in the delivery of the right metal to the protein (e.g., Urease).
Binding of nickel to a protein blocks binding of nickel to other proteins.

$[Fe-S]$ clusters are directed to the mitochondria.
Copper is in the Golgi instead of the cytosol.
Storage occurs in the vacuole (plants and fungi).
Cyanobacteria contain two enzymes, MncA and CucA, that are structurally identical but contain different metals. Both proteins are active in the periplasm.
There is no free copper in the cytosol but there is copper in the periplasm.