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| 1 | +[Meeting note](https://www.dropbox.com/s/ebpsm4r1vqf635s/Shih%20Huan%20Summer%20project.pdf?dl=0) |
| 2 | + |
| 3 | +# [Protein aggregation](https://pubmed.ncbi.nlm.nih.gov/21842954/ "Cohen JCP") |
| 4 | +### Master equation |
| 5 | +$\frac{df(t,j)}{dt}=2m(t)k_+(f(t,j-1)-f(t,j))+2k_{off}(f(t,j+1)-f(t,j))-k_-(j-1)f(t,j))+2k_-\displaystyle{\sum_{i=j+1}^{\infty}}f(t,i)+k_2m(t)^{n2}M(t)\delta_{j,n_2}+k_nm(t)^{n_c}\delta_{j,n_c}$ |
| 6 | + |
| 7 | + |
| 8 | +### Equations for the moments (similar notation as Georg's thesis): |
| 9 | +$\frac{dP(t)}{dt}=k_-[M(t)-(2n_c-1)P(t))]+k_2m(t)^{n_2}M(t)+k_nm(t)^{n_c} |
| 10 | +\\\coloneqq \alpha_0P(t)+\beta_0(t)M(t)+c(t)$ |
| 11 | + |
| 12 | +$\frac{dM(t)}{dt}=2[m(t)k_+-k_{off}-k_-n_c(n_c-1)/2]P(t)+n_2k_2m(t)^{n_2}M(t)+n_ck_nm(t)^{n_c} |
| 13 | +\\\coloneqq \alpha_1P(t)+\beta_1(t)M(t)+n_cc(t)$ |
| 14 | + |
| 15 | +### Solutions to the master equation |
| 16 | +>*Assumption:* |
| 17 | +>1. *the monomer concentration is constant.* |
| 18 | +>1. *monomer-dependent secondary nucleation is negligible* |
| 19 | +
|
| 20 | +$\frac{dP_0(t)}{dt}=k_-[M_0(t)-(2n_c-1)P_0(t))]+k_nm(0)^{n_c}$ |
| 21 | + |
| 22 | +$\frac{dM(t)}{dt}=2[m(0)k_+-k_{off}-k_-n_c(n_c-1)/2]P_0(t)+n_ck_nm(0)^{n_c}$ |
| 23 | + |
| 24 | +The solution is |
| 25 | + |
| 26 | +$$P_0(t)=C_1e^{\kappa_1t}+C_2e^{\kappa_2t}-\frac{\eta_2}{\xi_2}$$ |
| 27 | + |
| 28 | +$$M_0(t)=\frac{C_1\xi_2}{\kappa_1}e^{\kappa_1t}+\frac{C_2\xi_2}{\kappa_2}e^{\kappa_2t}-\frac{\eta_1}{k_-}-\frac{\xi_1\eta_2}{\xi_2}$$ |
| 29 | +, where |
| 30 | + |
| 31 | +$\kappa_{1,2}=\frac{1}{2}(-k_-\xi_1\pm\sqrt{k^2_-\xi^2_1+4k_-\xi_2})$ |
| 32 | + |
| 33 | +$\xi_1=2n_c-1$ |
| 34 | + |
| 35 | +$\xi_2=2m(0)k_+-2k_{off}-k_-n_c(n_c-1)$ |
| 36 | + |
| 37 | +$\eta_1=k_nm(0)^{n_c}$ |
| 38 | + |
| 39 | +$\eta_2=n_ck_nm(0)^{n_c}$ |
| 40 | + |
| 41 | +$C_{1,2}=\frac{1}{1-\frac{\kappa_{2,1}}{\kappa_{1,2}}}(\frac{\eta_2}{\xi_2}-\frac{\eta_1\kappa_{2,1}}{k_-\xi_2}-\frac{\xi_1\eta_2\kappa_{2,1}}{\xi_2^2}+P(0)-M(0)\frac{\kappa_{2,1}}{\xi_2})$ |
| 42 | + |
| 43 | +>*Here, we make a further assumption:* |
| 44 | +>1. *$m(0)k_+>>k_-$* |
| 45 | +
|
| 46 | +Hence, |
| 47 | + |
| 48 | +$\xi_2\approx 2[m(0)k_+-k_{off}]$ |
| 49 | + |
| 50 | +$\kappa_{1,2}\approx \pm\frac{1}{2}\sqrt{k^2_-\xi^2_1+4k_-\xi_2}\approx \pm\sqrt{k_-\xi_2}=\pm\sqrt{2[m(0)k_+-k_{off}]k_-}\coloneqq\pm\kappa$ |
| 51 | + |
| 52 | +$P_0(t)=C_1e^{\kappa t}+C_2e^{-\kappa t}-\frac{n_ck_nm(0)^{n_c}}{2[m(0)k_+-k_{off}]}$ |
| 53 | + |
| 54 | +$M_0(t)=\frac{C_12[m(0)k_+-k_{off}]}{\kappa}e^{\kappa t}-\frac{C_22[m(0)k_+-k_{off}]}{\kappa}e^{-\kappa t}-\frac{k_nm(0)^{n_c}}{k_-}$ |
| 55 | + |
| 56 | +$C_{1,2}\approx \frac{1}{2}(P(0)\pm\frac{\kappa M(0)}{2[m(0)k_+-k_{off}]}\pm \frac{\kappa k_nm(0)^{n_c}}{2[m(0)k_+-k_{off}]k_-})$ |
| 57 | + |
| 58 | +### Analysis of limiting cases |
| 59 | + |
| 60 | +### Analysis of the central moments |
| 61 | + |
| 62 | +#### Mean filament length |
| 63 | +$\mu(t)=\frac{M(t)}{P(t)}$ |
| 64 | + |
| 65 | +>At early times in *growth* phase, when the monomer concentration is held constant, denoted by a subscript 0, |
| 66 | +
|
| 67 | +$\mu_0(t)=\frac{2[k_+m(0)-k_off]}{\kappa}tanh(\frac{\kappa t}{2})$ |
| 68 | + |
| 69 | +For long time, |
| 70 | + |
| 71 | +$\mu_0(\infty)=\frac{2[k_+m(0)-k_off]}{\kappa}=\frac{2[k_+m(0)-k_off]}{\sqrt{2[m(0)k_+-k_{off}]k_-}}=\sqrt{\frac{2[m(0)k_+-k_{off}]}{k_-}}$ |
| 72 | + |
| 73 | +>When $k_+m(0)>>k_{off}$ |
| 74 | +
|
| 75 | +$\mu_0(\infty)=\sqrt{\frac{2m(0)k_+}{k_-}}$ |
| 76 | + |
| 77 | +> At later times, as the monomer is depleted, the full nonlinear solutions for M(t) and P(t ) show that the length decreases due to fragmentation dominating over [elongation](https://drive.google.com/file/d/1Zsb-pEJCJipKvLfSNm7JHBHA3KU5va7M/view?usp=sharing "time evolution of average length"). |
| 78 | +
|
| 79 | + |
| 80 | +### Convert Gillespie to bulk rates |
| 81 | +The units of concentation and rate constant in Gillespie are $_gC=(molecules)$ and $_gk=(time)^{-1}(molecule)^{-n}$. There is lack of volume term is unit. he relevant volume should be the cell volume $(10^{-5}m)^3\approx 1pl$. |
| 82 | +#### Concentration |
| 83 | +To convert Gillespie concentration to real concentration, we do the following calculation |
| 84 | +$$C={_g}C*\frac{1}{VN_0}={_g}C*\frac{10^{12}}{6\times10^{23}}$$ |
| 85 | + |
| 86 | +According to experiments, concentrations of protein aggregates are in the range of $$10^{-9}M<C<10^{-5}M$$ |
| 87 | +Hence, $$600<{_gC}<6000000$$ |
| 88 | +#### Rate constant |
| 89 | +Typical $k_+ =3\times10^{6}M^{-1}s^{-1}$, $k_+ = {_g}k*VN_0$. |
| 90 | + |
| 91 | +Hence, $_gk_+=5*10^{-6}s^{-1}(molec.)^{-1}$ |
| 92 | + |
| 93 | +$k_{off} =10^{-14}(sec)^{-1}$ |
| 94 | + |
| 95 | +Similarly, $_gk_n=5*10^{-16}s^{-1}(molec.)^{-1}$, $_gk_-=10^{-8}s^{-1}=k_-$, $k_2 = 10^4M^{-2}s^{-1}$ is equivalent to $k_- = 10^{-8}s^{-1}$ at $1\mu M$. |
| 96 | + |
| 97 | +### Estimate the simulation time |
| 98 | +From the [performance test](https://docs.google.com/spreadsheets/d/1CLMphbjoKtfBzVSIach01P74-mYVi8oHnucBW3zwJ0Y/edit?usp=sharing), to simulate a total fibril length of 20, it requires 100s. |
| 99 | +To scale to a longer fibril, the time requires |
| 100 | +$$c\times(20)^2=100s$$ |
| 101 | +$$c\times(10^5)^2=2\times10^9s\approx5.5\times10^5hr\approx63yr$$ |
| 102 | +for size = 10000 fibril. |
| 103 | + |
| 104 | +---- |
| 105 | + |
| 106 | +Simulation conditions: |
| 107 | + |
| 108 | +$_gk_+=5*10^{-8}s^{-1}(molec.)^{-1}$ |
| 109 | + |
| 110 | +$_gk_n=5*10^{-16}s^{-1}(molec.)^{-1}$ |
| 111 | + |
| 112 | +$_gk_- = 10^{-6}s^{-1}$ at $1\mu M$. |
| 113 | + |
| 114 | +$_gk_{off} =10^{-14}(sec)^{-1}$ |
| 115 | + |
| 116 | +$600<{_gC}=m_0<6000000$ |
| 117 | + |
| 118 | +Expected average length = $\sqrt{\frac{k_+m}{k_-}}= \sqrt{\frac{0.00000005*100000}{0.000001}}\approx 70$ |
| 119 | + |
| 120 | + |
| 121 | +$t = 10000000s, steps = 100$ |
| 122 | + |
| 123 | +Number of trajectories = $50$ |
| 124 | + |
| 125 | +Command line: |
| 126 | +> python Trial_of_fibril.py -kn 0.0000000000000005 -k+ 0.00000005 -k- 0.000001 -t 10000000 -s 100 -m *variable* -si *variable* -nc 2 |
| 127 | +
|
| 128 | +Results: |
| 129 | + |
| 130 | +|Test|k+|k-|kn|koff|Monomer|mu|simu_time|Time lapsed(s)| |
| 131 | +|--|--|--|--|--|--|--|--|--| |
| 132 | +|[1](https://drive.google.com/drive/folders/1tfLI7LaKOBCA7KZ02mXJ8B9CVynnTW5x?usp=sharing)|5e-07|1e-5|5e-12|1e-14|10000|31|10kappa^-1|82| |
| 133 | +|[2](https://drive.google.com/drive/folders/1PSzZkhybYjH4cKAqt495gqDukM8HQreZ?usp=sharing)|5e-08|1e-6|5e-13|1e-14|10000|31|10kappa^-1|78| |
| 134 | +|[3](https://drive.google.com/drive/folders/1wGQPBlnAReI3hkU3TecssuA7qowlsLqw?usp=sharing)|5e-08|1e-6|5e-15|1e-14|10000|31|100kappa^-1|73| |
| 135 | +|[4](https://drive.google.com/drive/folders/1rH8IpQdwlV0gglCmh1GUn4TsqLpJzo4_?usp=sharing)|5e-08|1e-6|5e-16|1e-14|10000|31|100kappa^-1|43| |
| 136 | +|[5](https://drive.google.com/drive/folders/1P3tyLJB9chWP5PCb9D1GzxJF3JsdrnwR?usp=sharing)|5e-08|1e-6|5e-16|1e-14|20000|44|10kappa^-1|129| |
| 137 | +|[6](https://drive.google.com/drive/folders/12uOOCnkXwTl5msmmuuLSpDyvUGY1meXu?usp=sharing)|5e-08|1e-6|5e-16|1e-14|20000|44|100kappa^-1|176| |
| 138 | + |
| 139 | +|Test|k+|k-|kn|koff|Monomer|mu|simu_time|Time lapsed(s)| |
| 140 | +|--|--|--|--|--|--|--|--|--| |
| 141 | +|[1](https://drive.google.com/file/d/1UvCaYXt1UvvNvfgn9x7DK_-Y8iwu0iqE/view?usp=sharing)|5e-07|1e-5|5e-12|1e-14|1000|10|30kappa^-1|4| |
| 142 | +|[2](https://drive.google.com/file/d/12jvMo0A_zDzqzVCncRZhq9VVLwTPr7be/view?usp=sharing)|5e-07|1e-5|5e-12|1e-14|10000|31|30kappa^-1|82| |
| 143 | +|[3](https://drive.google.com/file/d/1GqySia9hsL-M-e9Wd6NKg-eVddrltNCc/view?usp=sharing)|5e-07|1e-5|5e-12|1e-14|20000|44|30kappa^-1|117| |
| 144 | + |
| 145 | + |
| 146 | +### Fibril length coarse-graining - bulk --> This part does not have a conclusion |
| 147 | + |
| 148 | +### Fibril length coarse-graining - stochastic |
| 149 | + |
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