מדידה<em> במבחנה</em> פעילות ATPase עבור אנזימתי אפיון
Summary
We describe a basic protocol for quantitating in vitro ATPase activity. This protocol can be optimized based on the level of activity and requirements for a given purified ATPase.
Abstract
אנזימים אדנוזין hydrolyzing-אדנוזין, או ATPases, לשחק תפקיד קריטי במגוון תחומי פעילות התאים. חלבונים דינמיים אלה יכולים לייצר אנרגיה לעבודה מכאנית, כגון סחר חלבון ושפלה, תחבורה מומסת, ותנועות הסלולר. הפרוטוקול המתואר כאן הוא assay בסיסי למדידת הפעילות חוץ גופייה של ATPases המטוהר עבור אפיון פונקציונלי. חלבונים hydrolyze ATP בתגובה כי התוצאות שחרור פוספטים אנאורגניים, ואת כמות פוספט שוחררה לאחר מכן ונרשמת באמצעות assay colorimetric. ניתן להתאים מאוד זה פרוטוקול להתאמה כדי למדוד את פעילות ATPase מבחני קינטית או נקודת הסיום. פרוטוקול נציג מסופק כאן מבוסס על פעילות ודרישות של EpsE אא"א + ATPase מעורב Type II הפרשת ב החיידק Vibrio cholerae. כמות החלבון מטוהר צורך למדוד פעילות, האורך של assay ואת העיתוי מספר saבמרווחי mpling, חיץ רכב מלח, טמפרטורה, שיתוף גורמים, ממריצים (אם בכלל), וכו 'עשוי להשתנות מאלו המתוארים כאן, וכך כמה אופטימיזציה עשוי להיות נחוץ. פרוטוקול זה מספק מסגרת בסיסית ATPases המאפיינת וניתן לבצעו במהירות להתאים בקלות במידת הצורך.
Introduction
ATPases are integral enzymes in many processes across all kingdoms of life. ATPases act as molecular motors that use the energy of ATP hydrolysis to power such diverse reactions as protein trafficking, unfolding, and assembly; replication and transcription; cellular metabolism; muscle movement; cell motility; and ion pumping1-3. Some ATPases are transmembrane proteins involved in transporting solutes across membranes, others are cytoplasmic and may be associated with a biological membrane such as the plasma membrane or those of organelles.
AAA+ ATPases (ATPases associated with various cellular activities) make up a large group of ATPases that share some sequence and structural conservation. These proteins contain conserved nucleotide binding motifs such as Walker-A and -B boxes and form oligomers (generally hexamers) in their active state1. Large conformational changes in these proteins upon nucleotide binding have been characterized among diverse members of the AAA+ family. EpsE is a AAA+ ATPase and member of the bacterial Type II/IV secretion subfamily of NTPases4-6. EpsE powers Type II Secretion (T2S) in Vibrio cholerae, the causative agent of cholera. The T2S system is responsible for the secretion of a wide variety of proteins, such as the virulence factor cholera toxin that causes profuse watery diarrhea when V. cholerae colonizes the human small intestine7.
Techniques for quantitating in vitro ATPase activity are varied, but commonly measure phosphate release using colorimetric, fluorescent, or radioactive substrates8-11. We describe a basic method for determining in vitro ATPase activity of purified proteins using a colorimetric assay based on a commercially available malachite green-containing substrate that measures liberated inorganic phosphate (Pi). At low pH, malachite green molybdate forms a complex with Pi and the level of complex formation can be measured at 650 nm. This simple and sensitive assay may be used to functionally characterize new ATPases and to evaluate the roles of potential activators or inhibitors, to determine the importance of domains and/or specific residues, or to assess the effect of particular treatments on enzymatic activity.
Protocol
Representative Results
Discussion
זהו פרוטוקול כללי למדידת בפעילות ATPase במבחנה של חלבונים מטוהרים לאפיון ביוכימיים. שיטה זו מותאמת במיוחד בקלות; למשל, התאמת כמות חלבון, חיץ ויצירות מלח, טמפרטורה, וגיוון האורך ומרווחי assay (כולל הגדלת המספר הכולל של מרווחים) יכול לשפר quantitation פעילות. זמין מסחרי ר…
Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors would like to acknowledge funding from a National Institutes of Health grant RO1AI049294 (to M. S.).
Materials
| HEPES buffer | Fisher | BP310-500 | |
| Sodium chloride | Fisher | BP358-212 | |
| Magnesium chloride | Fisher | BP214-500 | |
| Adenosine triphosphate (ATP) | Fisher | BP41325 | |
| 96-well plates (clear, flat-bottom) | VWR | 82050-760 | |
| BIOMOL Green | Enzo Life Sciences | BML-AK111 | Preferred phosphate detection reagent. Caution: irritant. |
| Microplate reader | BioTek Synergy or comparable | ||
| Prism 5 | GraphPad Software | ||
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