CRISPR is too fat for many therapies so scientists are putting the

first_imgThe Cas9 enzyme, key to the CRISPR system, has a lot of fat that it can lose and still serve as a powerful tool. Click to view the privacy policy. Required fields are indicated by an asterisk (*) Sign up for our daily newsletter Get more great content like this delivered right to you! Country CRISPR is too fat for many therapies, so scientists are putting the genome editor on a diet Meletios Verras/shutterstock.com By Jon CohenAug. 30, 2018 , 8:00 AMcenter_img Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe Savage, a structural biologist who presented his group’s work last week at the annual Cold Spring Harbor Laboratory CRISPR meeting here, calls the protein engineering method Minimization by Iterative Size-Exclusion Recombination (MISER). The technique uses two enzymes to systematically snip the DNA of the SpCas9 gene, pulling out chunks encoding different parts of the protein. Savage and colleagues then test those genetic sequences to see whether their resultant proteins still retain Cas9’s ability to bind to DNA targets. They then combine the ones that succeed, to add to the unique truncated options. So far, they have made half a million variants. “Shockingly, it works really well,” Savage says. “I didn’t expect it to be so flexible that it could tolerate enormous deletions and those could be stacked together.”The MISER mutants won’t necessarily be able do everything that the typical CRISPR-Cas9 system can. One handicap is that some of the mutant Cas9s can lock onto an exact spot in the genome but cannot cut the DNA. But researchers earlier found that these “dead” Cas9s are handy tools, too, as they can ferry other molecules to specific destinations; one particularly powerful CRISPR technology called base editing exploits this to shuttle an enzyme to a target site that can convert one DNA base into another. The smallest MISER Cas9 mutant created to date—which can’t cut—has only 880 amino acids, about two-thirds the size of the original SpCas9.Harvard University chemist David Liu, whose lab invented the base editor system, says Savage’s work with MISER is an “an outstanding early application of this exciting new method—and moves the genome editing field closer to a long-standing goal.”Many investigators using CRISPR to design biomedical treatments package the genes for Cas9 and its other component inside a harmless virus that can shuttle them to specific cells to repair genetic defects. But the viruses have a limit to how much genetic cargo they can carry, and that’s where the skinny Cas9 could help tremendously—especially if its scissors work. “We have to finish this story,” says Savage, whose team is now sifting through its creations to find out which ones get the biggest bang for the smallest size. COLD SPRING HARBOR, NEW YORK—The genome editor CRISPR has morphed over the past 6 years from an obscure bacterial immune mechanism into the rock star tool of biology, allowing researchers to alter DNA with greater precision and ease than ever before. But the most popular version of CRISPR is simply too big, which complicates reaching some targets—and limits the ability of this powerful technology to create new therapies. Now, researchers have devised a way to put CRISPR on a diet and still retain its core functions.Standard CRISPR methods have appropriated a DNA-snipping protein called SpCas9 from the Streptococcus pyogenes bacterium. Another CRISPR component guides the enzyme to targeted places on the genome. SpCas9 binds the DNA and its molecular scissors clip the double-stranded helix. But this lab darling, which has 1368 amino acids, is too chunky for many biomedical applications. So a team led by David Savage of the University of California, Berkeley, has devised a huge library of slimmer Cas9s using a “directed evolution” scheme.“This is an amazing story because it’s a reversal of the actual evolutionary process,” says Kira Makarova, a pioneering CRISPR researcher at the National Center for Biotechnology Information in Bethesda, Maryland, who was not involved in the new work. Emaillast_img read more