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This is a throwback puzzle to the early days of Foldit. This protein is found on the surface of bacteriophage fd, a virus that infects E. coli. It is responsible for penetrating the cell membrane of the host bacteria, allowing virus to enter the cell. This protein contains four cysteines that oxidize to form two disulfide bonds. We are revisiting old Foldit puzzles so we can see how useful the recent additions to the game have been, and to provide newer players with easier puzzles that are still scientifically relevant.

Fold the transposase protein into a density map! This is a followup to Puzzle 1784: CRISPR-Cas Transposase Part I, now with a cryo-EM density map! Players may load in previous work from Puzzle 1784.

Design a symmetric trimer, with 3 identical chains that assemble together! This puzzle includes a Secondary Structure Objective so that no more than 50% of residues may form helices. The H-bond Network Objective encourages players to bury satisfied H-bond networks at the interface between symmetric chains. H-bond networks are a great way to introduce polar residues at the interface, but it's important that all of the bondable atoms make hydrogen bonds! In this puzzle, there are no limits on the Complex Core, but we've included the Complex Core objective so players can see which residues count as core in the H-bond Networks.

This is a throwback puzzle to the early days of Foldit. This small disulfide-rich protein is produced by the moth H. virescens as a defense against certain bacterial and fungal infections. This protein contains six cysteines that oxidize to form three disulfide bonds. We are revisiting old Foldit puzzles so we can see how useful the recent additions to the game have been.

This is the eighth puzzle in the poly-proline helix design series! The starting structure is slightly longer than previous rounds, with a 90 residue protein and a 6 residue helix. All residues are mutable, and we have reset the proline reference energy to 16.4 to allow for a greater diversity of residues. Keeping all buried polars satisfied is still a key component of a good structure, as well as a hydrophobic core and well defined secondary structures.

Design a symmetric trimer, with 3 identical chains that assemble together! This puzzle includes a Secondary Structure Objective so that no more than 50% of residues may form helices. We're taking a short break from H-bond Networks, but we have a new (optional) challenge for Foldit players! The starting structure includes several helices and sheets placed in a suggested arrangement, similar to a TIM barrel (but with 9 strands instead of 8). This is a hypothetical fold that nobody has been able to design yet, but we think Foldit players may have some ideas! Note that the started arrangement is only a rough placement, we expect players will have to do some considerable refolding to create a high-scoring design. For such a fold to work, it's important that the sheets of one subunit will need to pair with the symmetric sheets on either side, so that the entire barrel forms a continuous and circular hydrogen-bonded sheet!

This is a throwback puzzle to the early days of Foldit. This small domain is part of a larger protein found at high concentrations of the lens of the eye; historically, this protein was purified from the eyes of B. taurus for research. The protein is modeled here in reduced state, so no disulfides are expected to form. We are revisiting old Foldit puzzles so we can see how useful the recent additions to the game have been.

This is the seventh puzzle in the poly-proline helix design series! The starting structure is an 80 residue protein with a 5 residue helix, and all residues are mutable. The reference weight fo proline has been changed from 16.4 to 30.0 to provide a small incentive for proline usage. Keeping good hydrophobic cores with any buried polars satisfied with hydrogen bonds will help create stable structures. Hydrogen bonds are visible by selecting 'Show advanced GUI' in General Options in the Menu tab, and then selecting 'Show bonds (loop)' and 'Show bondable atoms' in the View tab.

Fold this transposase protein from a CRISPR-Cas complex! This puzzle presents the second half of the transposase protein, as a follow-up to Puzzle 1784: CRISPR-Cas Transposase Part I.

This is a throwback puzzle to the early days of Foldit. This protein is secreted at the site of inflammation, recruiting monocytes and T cells to help fight an infection. This protein contains four cysteine residues that oxidize to form two disulfide bonds. We are revisiting old Foldit puzzles so we can see how useful the recent additions to the game have been.