Cas9 image 0290 [smll].jpg

Cas9  [CRISPR]
2018
Stained glass
29" h x 29" w

Gene editing, especially in humans, has been the subject of ethical questions long before it became feasible.  This artwork shows the crystal structure of Cas9 - the enzyme that has made gene editing for human diseases a reality - in clinical trials and for a limited and special subgroup of such diseases at this time…until November, 2018, when a Chinese scientist reported he had “secretly” used CRISPR to edit fertilized human egg cells and implanted them, possibly leading to gene-edited babies, and triggering an ethical backlash from the scientific community.

Whereas some of these stained glass works have a pattern of symmetry and/or flow, this one is frenetic and may seem to have no obvious pattern.  It resembles a random collection of cylinders with an explosive quality, but which also seem to be caught floating like a "moment in time."  There’s a parallel with the actual Cas9, the enzyme that potentially could cause explosive havoc with an organism’s DNA, but which amazingly finds its way to a “moment in space” – the target site. (The multicolored, winding stripes represent the enzyme's guide RNA, and target DNA.)

 

Scientific Background

A bacterial defense mechanism against bacterial viruses, the enzyme "Cas9" can attack or alter the infecting viral DNA.  Bacteria infected with viruses store fragments of viral DNA, inserting them in their own DNA in sites known as "clustered regularly interspaced short pallidromic repeats." The acronym for these sites, C-R-I-S-P-R, has come to refer to the whole process of Cas9 mediated gene editing.  Cas9 uses these saved bits of viral genome in the form of "guide" RNA (twisted, multicolored band in the artwork) to search for, target, and destroy viral DNA from any repeat infection of the same virus.  Cas9 has been adapted by researchers for therapeutic purposes by designing guide RNAs which target genes responsible for genetic diseases, with the goal of repairing these gene or replacing them with normal genes.  Researchers substitute a different guide RNA, e.g., one corresponding to a defective human gene, and seek to use a form of the enzyme to destroy, modify, or correct this gene in the setting of human cells.

The crystal structure of Cas9 from Streptococcus pyogenes and its accompanying RNA and DNA, shown in this stained glass piece, is based on PDB (Protein Data Bank) file 4008.  The research was published in a paper in Cell 156, 935-949, 2014, by Hiroshi Nishimasu, F. Ann Ran, Patrick D. Hsu, Silvana Konermann, Sraya I. Shehata, Naoshi Dohmae, Ryuichiro Ishitani, Feng Zhang, and Osamu Nureki.  The cylinders represent helical regions of the protein. The 3' end of the RNA (multicolored, winding stripe) is at the bottom of the image.  The shorter stripe of 18 bases (right side) is DNA.  Different structural and functional regions of the protein (domains) are color coded: Rec1 (shown in blues), Rec2 (purples), HNH (pink), RuvC (reds), PI (greens), and Bridge Helix (lime green).  The enzyme comprises two lobes - the recognition (REC) lobe (consisting of the Rec1 region, the bridge helix, and the Rec2 domain) and the nuclease (NUC) lobe (the RuvC region, HNH region, and PAM-interaction (PI) region) (see paper for further details.) 

The DNA/RNA bases are color coded: Adenine: azure; Thymine: turquoise(dark); Guanine: grape; Cytosine: copper; Uracil: turquoise (light). A few bases are hidden or partially hidden behind protein or DNA/RNA.  For this artwork, the bases were deliberately chosen for DNA in order to encode (5'to 3') the amino acid sequence cysteine - arginine - isoleucine - serine - proline - arginine, or in single letter abbreviations, CRISPR.

The sequence of the unbound RNA (5' to 3') was chosen to encode the following amino acid sequence:  histidine - asparagine - phenylalanine - alanine - arginine - proline - aspartate - histidine - serine - lysine - serine - isoleucine - serine - asparagine - aspartate - arginine - isoleucine - phenylalanine - glutamate - glutamine - asparagine - stop - lysine.  The curious reader may try to decipher the hidden significance of this sequence.  (Hint: Q is substituted for O and E chosen for Z.)