Structural diversity of polyoxomolybdate clusters along the three-fold axis of the molybdenum storage protein

• Published in: Journal of inorganic biochemistry Vol. 138; pp. 122 - 128
• Main Authors: Poppe, Juliane, Warkentin, Eberhard, Demmer, Ulrike, Kowalewski, Björn, Dierks, Thomas, Schneider, Klaus, Ermler, Ulrich
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2014
• Subjects: Azotobacter vinelandii; Azotobacter vinelandii - chemistry; Bacterial Proteins - chemistry; Binding Sites; Crystal structure; Metalloproteins - chemistry; Molybdenum - chemistry; Molybdenum - metabolism; Molybdenum storage protein; Polyoxometalate; Protein Binding; Template; DODWOZOGBJDNFR-UHFFFAOYSA-N; Polyoxometalate; ARKZKBHYASPLQF-UHFFFAOYSA-H; Azotobacter vinelandii; ZZVGNGIOFMANET-UHFFFAOYSA-A; Molybdenum storage protein; Template; Crystal structure
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/j.jinorgbio.2014.05.009

The molybdenum storage protein (MoSto) can store more than 100 Mo or W atoms as discrete polyoxometalate (POM) clusters. Here, we describe the three POM cluster sites along the threefold axis of the protein complex based on four X-ray structures with slightly different polyoxomolybdate compositions between 1.35 and 2Å resolution. In contrast to the Moα-out binding site occupied by an Mo3 cluster, the Moα-in and Moβ binding sites contain rather weak and non-uniform electron density for the Mo atoms (but clearly identifiable by anomalous data), suggesting the presence of POM cluster ensembles and/or degradation products of larger aggregates. The “Moα-in cluster ensemble” was interpreted as an antiprism-like Mo6 species superimposed with an Mo7 pyramide and the “Moβ cluster ensemble” as an Mo13 cluster (present mostly in a degraded form) composed of a pyramidal Mo7 and a Mo3 building block linked by three spatially separated MoOx units. Inside the ball-shaped Mo13 cluster sits an occluded central atom, perhaps a metal ion. POM cluster formation at the Moα-in and Moβ sites appears to be driven by filtering out and binding/protecting self-assembled transient species complementary to the protein template. Nature developed a special protein that stores Mo as compact polyoxomolybdate (POM) clusters. The 1.35Å X-ray structure revealed reliable electron density for two new POM cluster ensembles along the threefold axis. The protein template wraps the new POM clusters, thereby determines their complementary structure and suppresses their hydrolysis. [Display omitted]