Solution Structure And Constrained Molecular Dynamics Study Of Vitamin B12 Conjugates Of The Anorectic Peptide PYY(3-36)

#50, published in ChemMedChem (11 (2016), 9, 1015-1020), DOI:cmdc.201600073.

The key to molecular dynamics simulations is recycling – specifically, going into a first project with enough organization to know how to use everything in the next study. While that first successful connectivity table, parameter assignment, and RESP charge generation for something as Frankenstein-esque as vitamin B12 is the north face of Everest, that next simulation is simply a matter of having atom codes in your PDB file standardized.

And, speaking of PDBs, article #50 has the added bonus of having its own entry in the Protein Databank as 2NA5 – quite a treat (to me, anyway).

And furthermore, this is the first of my publications to benefit from the Research Computing infrastructure on the Syracuse University campus – the throughput of calculations for future work is completely unprecedented in my history of resource access anywhere (the drop in storage prices is very real to some of us).


Authors: Henry K.E., Kerwood D.J., Allis D.G., Workinger J.L., Bonaccorso R.L., Holz G.G., Roth C.L., Zubieta J., and Doyle R.P.

Abstract: Vitamin B12–peptide conjugates have considerable therapeutic potential through improved pharmacokinetic and/or pharmacodynamic properties imparted on the peptide upon covalent attachment to vitamin B12 (B12). There remains a lack of structural studies investigating the effects of B12 conjugation on peptide secondary structure. Determining the solution structure of a B12–peptide conjugate or conjugates and measuring functions of the conjugate(s) at the target peptide receptor may offer considerable insight concerning the future design of fully optimized conjugates. This methodology is especially useful in tandem with constrained molecular dynamics (MD) studies, such that predictions may be made about conjugates not yet synthesized. Focusing on two B12 conjugates of the anorectic peptide PYY(3–36), one of which was previously demonstrated to have improved food intake reduction compared with PYY(3–36), we performed NMR structural analyses and used the information to conduct MD simulations. The study provides rare structural insight into vitamin B12 conjugates and validates the fact that B12 can be conjugated to a peptide without markedly affecting peptide secondary structure.

Examining The Effects Of Vitamin B12 Conjugation On The Biological Activity Of Insulin: A Molecular Dynamic And In Vivo Oral Uptake Investigation

Published in MedChemComm (direct link: And Happy Belated New Year. After the methodological work that went into the Molecular Biosystems paper, this was a remarkably simple molecular dynamics study of the changes to vitamin B12 binding in transcobalamin II (TCII) with the B12 conjugated to the first amino acid side chain in the B-Chain of insulin. The structure of the B12-insulin conjugate is shown below in a molecular dynamics snapshot, which reveals that the binding of B12 to its TCII transport protein is negligibly affected.

And apparently the experiments went well, too. Cover hopefully to follow.

Susan Clardy-James, Damian G. Allis, Timothy J. Fairchild and Robert P. Doyle

Abstract: The practical use of the vitamin B12 uptake pathway to orally deliver peptides and proteins is much debated. To understand the full potential of the pathway however, a deeper understanding of the impact B12 conjugation has on peptides and proteins is needed. We previously reported an orally active B12 based insulin conjugate attached at LysB29 with hypoglycaemic properties in STZ diabetic rats. We are exploring an alternative attachment for B12 on insulin in an attempt to determine the effect B12 has on the protein biological activity. We describe herein the synthesis, characterization, and purification of a new B12-insulin conjugate, which is attached between the B12 ribose hydroxyl group and insulin PheB1. The hypoglycemic properties resulting from oral administration (gavage) of such a conjugate in STZ diabetic rats was similar to that noted in a conjugate covalently linked at insulin LysB2911, demonstrating the availability of both position on insulin for B12 attachment. A possible rationale for this result is put forward from MD simulations. We also conclude that there is a dose dependent response that can be observed for B12-insulin conjugates, with doses of conjugate greater than 10-9 M necessary to observe even low levels of glucose drop.

Vitamin B12 In Drug Delivery: Breaking Through The Barriers To A B12 Bioconjugate Pharmaceutical

In press in Expert Opinion On Drug Delivery (DOI:10.1517/17425247.2011.539200). The theory section (the only part I can properly speak to) builds on the discussion section of the full theory paper in Molecular Biosystems from earlier this year, providing an outlet for some of the more speculative design possibilities for trinary B12 bioconjugate design. Given that (1) there are mechanisms for cleavage at both of the proposed positions and (2) the molecular dynamics work indicates that, at least, TCII (transcobalamin II) can easily accommodate a bi-functionalized cobalamin, the A-B12-C design possibility is probably the most interesting long-term idea to come out of the computational side of the B12-insulin bioconjugate study (or so I argue).

Having “B12” and “cobalamin” in a blog post guarantees a bunch of useless moderation-necessary comments from vita-spam sites.

Susan M. Clardy, Damian G. Allis, Timothy J. Fairchild & Robert P. Doyle

Syracuse University, Syracuse, Department of Chemistry, NY 13244-4100, USA

Importance of the field: Vitamin B12 (B12) is a rare and vital micronutrient for which mammals have developed a complex and highly efficient dietary uptake system. This uptake pathway consists of a series of proteins and receptors, and has been utilized to deliver several bioactive and/or imaging molecules from 99mTc to insulin.

Areas covered in this review: The current field of B12-based drug delivery is reviewed, including recent highlights surrounding the very pathway itself.

What the reader will gain: Despite over 30 years of work, no B12-based drug delivery conjugate has reached the market-place, hampered by issues such as limited uptake capacity, gastrointestinal degradation of the conjugate or high background uptake by healthy tissues. Variability in dose response among individuals, especially across ageing populations and slow oral uptake (several hours), has also slowed development and interest.

Take home message: This review is intended to stress again the great potential, as yet not fully realized, for B12-based therapeutics, tumor imaging and oral drug delivery. This review discusses recent reports that demonstrate that the issues noted above can be overcome and need not be seen as negating the great potential of B12 in the drug delivery field.

B12-Insulin Bioconjugate/Transcobalamin(II)/Insulin Receptor Cover Image For The April Issue Of Clinical Chemistry

A brief post about some free research press (and the new addition to the Cover Gallery). Having already been featured on the cover of the ChemMedChem March 2009 issue (see the New B12-Insulin-TCII-Insulin Receptor Cover Image For This Month’s ChemMedChem (March 2009) post) , the side-on view of the B12-Insulin/TCII/Insulin Receptor structure was chosen for this month’s cover of Clinical Chemistry. While the originating article itself is not included in the issue (I should have recommended citing the ChemMedChem article in the image caption), several diabetes-related articles are featured in this month’s issue.

ON THE COVER: Scientists are investigating ways to develop effective oral insulin therapies. One such model is a vitamin B12–insulin conjugate bound to transcobalamin II and is shown here docked in the insulin receptor. The discovery of easier ways to deliver insulin into the blood stream would improve the lives of the millions of individuals living with diabetes. This month’s issue of Clinical Chemistry contains 4 articles related to diabetes. The first 2 articles provide readers with a point/counterpoint discussion of the value of reporting estimated glucose along with Hb A1c. Next is an article on the association of apolipoprotein B with incident type 2 diabetes. Lastly, the development of the first radioimmunoassay for insulin led to a Nobel Prize and is chronicled in this month’s Citation Classic feature. (See pages 545, 547, 666, and 671.) Image reproduced with permission from Damian G. Allis and Robert P. Doyle, Department of Chemistry, Syracuse University.

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Exploring the Implications of Vitamin B12 Conjugation to Insulin on Insulin Receptor Binding and Cellular Uptake

In press, in the journal ChemMedChem (and, because I think it’s hip, I note that the current “obligatory” image for the wikipedia article for ChemMedChem features the image I made for the review article on the topic addressed in this new study). As with many theory papers (there’s some experiment in there, too), this very brief article summarizes several months of cyanocobalamin (B12) parameterization and molecular dynamics (MD) simulations. The purpose of the theory was to address all of the major structural snapshots in the uptake process associated with the insulin-B12 bioconjugate being developed as part of the much heralded oral insulin project in Robert Doyle’s group here at Syracuse. These structures include:

1. The structure and dynamic properties of the insulin-B12 bioconjugate
2. The binding of B12 to Transcobalamin II (TCII) (for B12 parameterization)
3. The binding of the insulin-B12 bioconjugate to TCII (and the steric demands therein)
4. The interaction of the insulin-B12 bioconjugate, bound to TCII, with the insulin Receptor (IR)

The quantum chemical (for the B12 geometry and missing force constants) and molecular dynamics (GROMACS with the GROMOS96 (53a6)) simulation work is going to serve as the basis for several posts here (eventually) about parameterization, topology generation, and force field development.

As an example of some of the insights modeling provides, the figure above shows the insulin-B12 bioconjugate (the insulin is divided into A and B chains, the A chain in blue and the important division of the insulin B chain in the front half of the rainbow). Insulin is a rather large-scale example of many of the same molecular issues that arise in the analysis of solid-state molecular crystals by either terahertz or inelastic neutron scattering spectroscopy. The packing of molecules in their crystal lattices can lead to significant changes in molecular geometry, be these changes in the stabilization of higher-energy molecular conformations or even deformations in the covalent framework. In the case of insulin, it is found that the crystal geometry (also the geometry of stored insulin in the body) is quite different from the solution-phase form. It’s even worse! The B chain end (B20-B30) in the solid-state geometry covers (protects?) the business-end of the insulin binding region to the Insulin Receptor. One can imagine the difficulty in proposing the original binding model for insulin to its receptor from the original crystal data given that the actual binding region is blocked off in the solid-state form! The “Extended” form in the figure is representative of “multiple other” conformations of the B20-B30 region (which mimics the characterized T-state of insulin), those geometries for which the insulin binding region (blue and green) is completely exposed. This extended geometry is also the one that separates the bulk of the insulin structure from the covalently-linked B12 (at Lys29) and, it is argued from the MD simulations in the paper, enables the B12 to still tightly bind to TCII despite the presence of all this steric bulk.

Amanda K. Petrus1, Damian G. Allis1, Robert P. Smith2, Timothy J. Fairchild3 and Robert P. Doyle1

1. Department of Chemistry, Syracuse University, Syracuse, NY 13244, USA
2. Department of Construction Management and Wood Products Engineering, SUNY, College of Environmental Science and Forestry, Syracuse, NY 13210, USA
3. Department of Exercise Science, Syracuse University, Syracuse, NY 13244, USA

Extract: We recently reported a vitamin B12 (B12) based insulin conjugate that produced significantly decreased blood glucose levels in diabetic STZ-rat models. The results of this study posed a fundamental question, namely what implications does B12 conjugation have on insulin’s interaction with its receptor? To explore this question we used a combination of molecular dynamics (MD) simulations and immuno-electron microscopy (IEM).

DNA-Specific (But Generally Applicable) AMBER With GROMACS 3.3.x: Installation And Notes

The following is the full procedure for installing the AMBER force field port for GROMACS (AMBER-in-GROMACS, AMBER-with-GROMACS, AMBER-on-GROMACS, whatever you want to call it) developed by Eric Sorin at California State University, Long Beach, providing a bit more depth in the installation process (specifically for GROMACS 3.3.x) and a few modified GROMACS files.

As brief background, AMBER (Assisted Model Building and Energy Refinement) is one of THE dominant molecular mechanics/molecular dynamics (MM/MD) force fields used today in biochemical simulations. The motivation for this page (my installing AMBER for use in GROMACS) stems from the current Nanorex focus on Structural DNA Nanotechnology (SDN) modeling, for which we’re working on a reduced model force field for large-structure energy minimizations and, importantly, integrating the GROMACS MM/MD package for use via our CAD interface. You can read more about this in the poster presented at FNANO08 this past April. As a force field validated for DNA simulations, AMBER meets our needs of performing atomistic simulations on DNA nanostructures. While NAMD is also a possibility for DNA simulations, GROMACS meets Nanorex’s open source needs.

Continue reading “DNA-Specific (But Generally Applicable) AMBER With GROMACS 3.3.x: Installation And Notes”