Peptide–Gold Nanoparticle Conjugates as Artificial Carbonic Anhydrase Mimics

Abstract

We herein describe the design and synthesis of a catalytically active peptide–gold nanoparticle conjugate (Pep-Au-NP) that binds Zn(II) within its peptide monolayer and develops carbonic anhydrase activity. Specifically, a modified variant of the β-sheet forming IHIHIQI-peptide (IHQ), which forms an interstrand 3-His Zn(II)-binding site, was used as a ligand for spherical gold nanoparticles (Au-NPs). The resulting immobilized peptide maintains its ability to form β-sheets, as determined by circular dichroism (CD)-spectroscopy and, thus, maintains its ability to form Zn(II)-binding sites. The addition of Zn(II)-ions to the peptide–gold nanoparticle conjugates (Au@IHQ-NP) resulted in significant improvements in rates of ester hydrolysis of 4-nitrophenyl acetate (4-NPA) and the hydration of CO2 compared to the unconjugated peptide variants. Recycling of the catalyst revealed that Au@IHQ-NP remains intact with at least 94% of its initial activity after five rounds of CO2 hydration. The herein reported results reveal that Pep-Au-NPs are able to perform reactions catalyzed by natural metalloenzymes and open up new possibilities for the implementation of these conjugates.

Catalytically Active Peptide–Gold Nanoparticle Conjugates: Prospecting for Artificial Enzymes

“…More interestingly,A u@IHQ-NP catalyzes the hydration of CO 2 with superior rates compared to the unconjugated peptide.T hus,r ate acceleration due to the development of ap eptide monolayer is not only limited to self-assembled systems with an internal peptide organization, but is extendable also to Pep-Au-NPs that form defined secondary structures and execute catalytic mechanisms by developed metal centers. [59] These results also strongly indicate that the catalytic rate enhancement of Pep-Au-NPs is not merely ac onsequence of ac hange in reaction mechanism, but is an effect evoked by am ore intricate set of interaction events that occur within the monolayer. Understanding these effects at the molecular level also proves beneficial for the design of Pep-Au-NPs for other applications in molecular recognition or binding of atarget molecule/ receptor.…”

“…[61] CD spectroscopy revealed that IHQ-NP assembles into bsheet structures,i ndicated by as ingle ellipticity minimum around 215 nm, also when conjugated to Au-NPs.T hus,t he prerequisite for the 3-His-Zn II center is fulfilled. [59] Au@IHQ-NP and its unconjugated variant IHQ-NP marginally catalyze the hydration of CO 2 to HCO 3 À in Tr is-buffered solution, in the absence of Zn II (Figure 7). Thea ddition of Zn II significantly increases rates of CO 2 hydration by 20 %and 50 %for IHQ-NP and Au@IHQ-NP,r espectively,c ompared to the buffer control.…”

Catalytically Active Peptide–Gold Nanoparticle Conjugates: Prospecting for Artificial Enzymes

“…More interestingly, Au@IHQ‐NP catalyzes the hydration of CO 2 with superior rates compared to the unconjugated peptide. Thus, rate acceleration due to the development of a peptide monolayer is not only limited to self‐assembled systems with an internal peptide organization, but is extendable also to Pep–Au‐NPs that form defined secondary structures and execute catalytic mechanisms by developed metal centers . These results also strongly indicate that the catalytic rate enhancement of Pep–Au‐NPs is not merely a consequence of a change in reaction mechanism, but is an effect evoked by a more intricate set of interaction events that occur within the monolayer.…”

“…Simultaneously, we wanted to prove that Pep–Au‐NPs are able to catalyze chemical reactions other than ester hydrolysis. Therefore, we designed a Pep–Au‐NP system that mimics the activity of the zinc‐containing metalloenzyme carbonic anhydrase (CA) . We extracted the design rules for Pep–Au‐NPs obtained from the E3HX series and utilized the brush‐like nature of the peptide monolayer to design a peptide that, after conjugation to Au‐NPs, develops a minimalistic version of the active site of CA, instead of mimicking only the catalytic center.…”

“…CD spectroscopy revealed that IHQ‐NP assembles into β‐sheet structures, indicated by a single ellipticity minimum around 215 nm, also when conjugated to Au‐NPs. Thus, the prerequisite for the 3‐His–Zn II center is fulfilled . Au@IHQ‐NP and its unconjugated variant IHQ‐NP marginally catalyze the hydration of CO 2 to HCO 3 − in Tris‐buffered solution, in the absence of Zn II (Figure ).…”