A novel eukaryotic factor for cytosolic Fe–S cluster assembly

Abstract

In the above article, the authors twice made the statement that Cfd1p was the first iron-sulfur cluster assembly factor to be found in the cytoplasm. Other recent publications have suggested that proteins that have been shown to function in Fe-S cluster assembly in mitochondria may exist at low levels in the cytoplasm (Land and Rouault, 1998; Tong and Rouault, 2000; Nakai et al, 2001). Since this article went to press, two additional papers have added to these findings (Tong et al, 2003; Nakai et al, 2004).While some investigators have questioned whether Cfd1p is indeed the first reported cytosolic Fe-S cluster assembly factor, we emphasize that the significance of our finding is in identifying a new class of cluster assembly factor whose localization is exclusively cytoplasmic and whose function is demonstrably cytoplasmic as well.

Structures of lipoyl synthase reveal a compact active site for controlling sequential sulfur insertion reactions

“…The presence of a serine residue as a naturally occurring ligand for a protein bound [4Fe-4S] cluster has not been previously observed, but a serine for cysteine site directed mutation has often been used to modulate or eliminate cluster activity [46][47][48][49][50][51]. Examination of the electron density near the auxiliary cluster ( Figure 3B) shows clear density for the serine ligand (Ser283) with a short Fe-O bond length (1.8 Å in the MTA complex), which likely reflects deprotonation of the serine ligand.…”

“…This cluster is held in place by three conserved cysteine residues [14] and an unanticipated ligand from close to the C-terminus, Ser283. Serine is previously unreported as a natural ligand for [4Fe-4S] clusters, although this residue has been introduced as a cluster ligand by site directed mutagenesis [46][47][48][49][50][51]. In the TeLipA2:SAH complex structure, the Ser283 alkoxy oxygen atom lies in close proximity to an additional metal atom, which because of its abundance in the crystallization medium (initially approximately 160 mM), has been modeled as a sodium ion (Na-O distance 2.5 Å, Figure 3B).…”

Analysis of iron–sulfur protein maturation in eukaryotes

“…This methodology allows convenient determination of soluble enzyme activities. Examples include cytosolic human aconitase (IRP1) in a yeast deletion mutant lacking mitochondrial aconitase 50 , cytosolic 15 or mitochondria-targeted 51 isopropylmalate isomerase (Leu1) in a yeast cell lacking or with low cytosolic Leu1. In addition to the introduction of suitable marker Fe/S proteins, such experiments show that central parts of both the ISC and CIA machineries do not exhibit pronounced target specificity for Fe/S proteins of one given compartment.…”

“…In addition to the introduction of suitable marker Fe/S proteins, such experiments show that central parts of both the ISC and CIA machineries do not exhibit pronounced target specificity for Fe/S proteins of one given compartment. 50,51 Incorporation of radioactive iron into Fe/S proteins in vivo. The pulse radiolabeling of yeast cells with 55 Fe provides a faithful assay for the estimation of the de novo biogenesis of Fe/S cluster-containing proteins in vivo 10 .…”

Interaction with Cfd1 Increases the Kinetic Lability of FeS on the Nbp35 Scaffold

“…These homologous proteins are members of the ApbC/Nbp35 subfamily of P-loop NTPases that is characterized by a conserved C-terminal ENMS sequence followed by a CX 2 C cysteine cluster (15,16). This C-terminal cysteine cluster confers the ability onto these proteins of binding a bridging [4Fe-4S] cluster between monomers and is essential for activity of both proteins (6,14). Nbp35 also has a cysteine cluster at the N terminus, a feature that distinguishes it from Cfd1 and allows the Nbp35 monomer to bind an additional [4Fe-4S] cluster (7,14).…”